Fix not animated gifs support

process.go

@@ -524,7 +524,7 @@ func processImage(ctx context.Context) ([]byte, error) {
 	}
 	defer C.clear_image(&img)
 
-	if imgtype == imageTypeGIF && po.Format == imageTypeGIF {
+	if imgtype == imageTypeGIF && po.Format == imageTypeGIF && vipsIsAnimatedGif(img) {
 		if err := transformGif(ctx, &img, po); err != nil {
 			return nil, err
 		}
@@ -682,6 +682,10 @@ func vipsArrayjoin(in []*C.struct__VipsImage, out **C.struct__VipsImage) error {
 	return nil
 }
 
+func vipsIsAnimatedGif(img *C.struct__VipsImage) bool {
+	return C.vips_is_animated_gif(img) > 0
+}
+
 func vipsImageHasAlpha(img *C.struct__VipsImage) bool {
 	return C.vips_image_hasalpha_go(img) > 0
 }

vips.h

@@ -148,6 +148,13 @@ vips_band_format(VipsImage *in) {
   return in->BandFmt;
 }
 
+gboolean
+vips_is_animated_gif(VipsImage * in) {
+  return( vips_image_get_typeof(in, "page-height") != G_TYPE_INVALID &&
+          vips_image_get_typeof(in, "gif-delay") != G_TYPE_INVALID &&
+          vips_image_get_typeof(in, "gif-loop") != G_TYPE_INVALID );
+}
+
 gboolean
 vips_image_hasalpha_go(VipsImage * in) {
 #if VIPS_SUPPORT_HASALPHA