avif: Disable all strict decoder checks

New libavif 0.9.1 apply some very strict standard compliance
checks by default. Unfortunately, it rejects many files made by
libheif-based apps (GIMP, ImageMagick) in the past.
libheif 1.12.0 (released on May 5, 2021) addressed the problem,
but it would be good to extend grace period, allowing other
projects and distributions to upgrade to fixed version.

src/imageformats/avif.cpp

@@ -97,6 +97,10 @@ bool QAVIFHandler::ensureDecoder()
 
     m_decoder = avifDecoderCreate();
 
+#if AVIF_VERSION >= 90100
+    m_decoder->strictFlags = AVIF_STRICT_DISABLED;
+#endif
+
     avifResult decodeResult;
 
     decodeResult = avifDecoderSetIOMemory(m_decoder, m_rawAvifData.data, m_rawAvifData.size);