Fix XCF parasites metadata in QImage and support to ICC profile

- Fix parasite "gimp-comment" not set due to null QImage
- Support to parasite "icc-profile" using Qt 5.14+ API
- Added parasite "gimp-image-metadata" as QImage metadata "XML:org.gimp.xml"
- Added a XCF with XML metadata and icc prifile embedded in autotest folder (generated by GIMP 2.10.30)
- Tested with Qt 5.15.2 and Qt 6.2.3 under Windows and Qt 6.2.3 under macOS

src/imageformats/xcf.cpp

@@ -16,8 +16,9 @@
 #include <QStack>
 #include <QVector>
 #include <QtEndian>
-#include <stdlib.h>
+#include <QColorSpace>
 
+#include <stdlib.h>
 #include <string.h>
 
 #include "gimp_p.h"
@@ -351,6 +352,8 @@ private:
         bool initialized; //!< Is the QImage initialized?
         QImage image; //!< final QImage
 
+        QHash<QString,QByteArray> parasites;    //!< parasites data
+
         XCFImage(void)
             : initialized(false)
         {
@@ -405,6 +408,7 @@ private:
     bool composeTiles(XCFImage &xcf_image);
     void setGrayPalette(QImage &image);
     void setPalette(XCFImage &xcf_image, QImage &image);
+    void setImageParasites(const XCFImage &xcf_image, QImage &image);
     static void assignImageBytes(Layer &layer, uint i, uint j);
     bool loadHierarchy(QDataStream &xcf_io, Layer &layer);
     bool loadLevel(QDataStream &xcf_io, Layer &layer, qint32 bpp);
@@ -665,6 +669,9 @@ bool XCFImageFormat::readXCF(QIODevice *device, QImage *outImage)
         return false;
     }
 
+    // The image was created: now I can set metadata and ICC color profile inside it.
+    setImageParasites(xcf_image, xcf_image.image);
+
     *outImage = xcf_image.image;
     return true;
 }
@@ -715,15 +722,15 @@ bool XCFImageFormat::loadImageProperties(QDataStream &xcf_io, XCFImage &xcf_imag
                 property.readBytes(tag, size);
 
                 quint32 flags;
-                char *data = nullptr;
+                QByteArray data;
                 property >> flags >> data;
 
-                if (tag && strncmp(tag, "gimp-comment", strlen("gimp-comment")) == 0) {
-                    xcf_image.image.setText(QStringLiteral("Comment"), QString::fromUtf8(data));
-                }
+                // WARNING: you cannot add metadata to QImage here because it can be null.
+                // Adding a metadata to a QImage when it is null, does nothing (metas are lost).
+                if(tag) // store metadata for future use
+                    xcf_image.parasites.insert(QString::fromUtf8(tag), data);
 
                 delete[] tag;
-                delete[] data;
             }
             break;
 
@@ -1234,6 +1241,77 @@ void XCFImageFormat::setPalette(XCFImage &xcf_image, QImage &image)
     image.setColorTable(xcf_image.palette);
 }
 
+/*!
+ * Copy the parasites info to QImage.
+ * \param xcf_image XCF image containing the parasites read from the data stream.
+ * \param image image to apply the parasites data.
+ * \note Some comment taken from https://gitlab.gnome.org/GNOME/gimp/-/blob/master/devel-docs/parasites.txt
+ */
+void XCFImageFormat::setImageParasites(const XCFImage &xcf_image, QImage &image)
+{
+    auto&& p = xcf_image.parasites;
+    auto keys = p.keys();
+    for (auto&& key : qAsConst(keys)) {
+        auto value = p.value(key);
+        if(value.isEmpty())
+            continue;
+
+        // "icc-profile" (IMAGE, PERSISTENT | UNDOABLE)
+        //     This contains an ICC profile describing the color space the
+        //     image was produced in. TIFF images stored in PhotoShop do
+        //     oftentimes contain embedded profiles. An experimental color
+        //     manager exists to use this parasite, and it will be used
+        //     for interchange between TIFF and PNG (identical profiles)
+        if (key == QStringLiteral("icc-profile")) {
+            auto cs = QColorSpace::fromIccProfile(value);
+            if(cs.isValid())
+                image.setColorSpace(cs);
+            continue;
+        }
+
+        // "gimp-comment" (IMAGE, PERSISTENT)
+        //    Standard GIF-style image comments.  This parasite should be
+        //    human-readable text in UTF-8 encoding.  A trailing \0 might
+        //    be included and is not part of the comment.  Note that image
+        //    comments may also be present in the "gimp-metadata" parasite.
+        if (key == QStringLiteral("gimp-comment")) {
+            value.replace('\0', QByteArray());
+            image.setText(QStringLiteral("Comment"), QString::fromUtf8(value));
+            continue;
+        }
+
+        // "gimp-image-metadata"
+        //     Saved by GIMP 2.10.30 but it is not mentioned in the specification.
+        //     It is an XML block with the properties set using GIMP.
+        if (key == QStringLiteral("gimp-image-metadata")) {
+            // NOTE: I arbitrary defined the metadata "XML:org.gimp.xml" because it seems
+            //       a GIMP proprietary XML format (no xmlns defined)
+            value.replace('\0', QByteArray());
+            image.setText(QStringLiteral("XML:org.gimp.xml"), QString::fromUtf8(value));
+            continue;
+        }
+
+#if 0   // Unable to generate it using latest GIMP version
+        // "gimp-metadata" (IMAGE, PERSISTENT)
+        //     The metadata associated with the image, serialized as one XMP
+        //     packet.  This metadata includes the contents of any XMP, EXIF
+        //     and IPTC blocks from the original image, as well as
+        //     user-specified values such as image comment, copyright,
+        //     license, etc.
+        if (key == QStringLiteral("gimp-metadata")) {
+            // NOTE: "XML:com.adobe.xmp" is the meta set by Qt reader when an
+            //       XMP packet is found (e.g. when reading a PNG saved by Photoshop).
+            //       I reused the same key because some programs could search for it.
+            value.replace('\0', QByteArray());
+            image.setText(QStringLiteral("XML:com.adobe.xmp"), QString::fromUtf8(value));
+            continue;
+        }
+#endif
+
+    }
+}
+
+
 /*!
  * Copy the bytes from the tile buffer into the image tile QImage, taking into
  * account all the myriad different modes.