avformat/utils: dont count attached pics toward the probesize

Such pics behave more like headers which we also dont count.
Fixes Ticket3146
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/utils.c

@@ -2846,9 +2846,10 @@ int avformat_find_stream_info(AVFormatContext *ic, AVDictionary **options)
                 goto find_stream_info_err;
         }
 
-        read_size += pkt->size;
-
         st = ic->streams[pkt->stream_index];
+        if (!(st->disposition & AV_DISPOSITION_ATTACHED_PIC))
+            read_size += pkt->size;
+
         if (pkt->dts != AV_NOPTS_VALUE && st->codec_info_nb_frames > 1) {
             /* check for non-increasing dts */
             if (st->info->fps_last_dts != AV_NOPTS_VALUE &&