protect realloc overflow

Originally committed as revision 18088 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/mxfdec.c

@@ -364,6 +364,8 @@ static int mxf_read_primer_pack(MXFContext *mxf)
 
 static int mxf_add_metadata_set(MXFContext *mxf, void *metadata_set)
 {
+    if (mxf->metadata_sets_count+1 >= UINT_MAX / sizeof(*mxf->metadata_sets))
+        return AVERROR(ENOMEM);
     mxf->metadata_sets = av_realloc(mxf->metadata_sets, (mxf->metadata_sets_count + 1) * sizeof(*mxf->metadata_sets));
     if (!mxf->metadata_sets)
         return -1;