add wxImage::SetType() and use it in animation decoders (#9639)

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@54932 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/common/gifdecod.cpp

@@ -122,6 +122,7 @@ bool wxGIFDecoder::ConvertToImage(unsigned int frame, wxImage *image) const
     // create the image
     wxSize sz = GetFrameSize(frame);
     image->Create(sz.GetWidth(), sz.GetHeight());
+    image->SetType(wxBITMAP_TYPE_GIF);
 
     if (!image->Ok())
         return false;