Do not use config.h in public header files (#1262)

Clients do not have this file and they do not have HAVE_CONFIG_H
set, so the header files must be independent of the compile time
configuration of supported formats.

taglib/mpeg/mpegfile.cpp

@@ -25,6 +25,10 @@
 
 #include "mpegfile.h"
 
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
 #include "id3v2framefactory.h"
 #include "tdebug.h"
 #include "tpropertymap.h"
@@ -323,12 +327,14 @@ ID3v1::Tag *MPEG::File::ID3v1Tag(bool create)
   return d->tag.access<ID3v1::Tag>(ID3v1Index, create);
 }
 
-#ifdef WITH_APE
 APE::Tag *MPEG::File::APETag(bool create)
 {
+#ifdef WITH_APE
   return d->tag.access<APE::Tag>(APEIndex, create);
-}
+#else
+  return nullptr;
 #endif
+}
 
 bool MPEG::File::strip(int tags, bool freeMemory)
 {

taglib/mpeg/mpegfile.h

@@ -26,10 +26,6 @@
 #ifndef TAGLIB_MPEGFILE_H
 #define TAGLIB_MPEGFILE_H
 
-#ifdef HAVE_CONFIG_H
-#include "config.h"
-#endif
-
 #include "tfile.h"
 #include "taglib_export.h"
 #include "tag.h"
@@ -270,7 +266,6 @@ namespace TagLib {
        */
       ID3v1::Tag *ID3v1Tag(bool create = false);
 
-#ifdef WITH_APE
       /*!
        * Returns a pointer to the APE tag of the file.
        *
@@ -289,7 +284,6 @@ namespace TagLib {
        * \see hasAPETag()
        */
       APE::Tag *APETag(bool create = false);
-#endif
 
       /*!
        * This will strip the tags that match the OR-ed together TagTypes from the