avformat/bethsoftvid: Check image dimensions before use

Fixes: signed integer overflow: 55255 * 53207 cannot be represented in type 'int'
Fixes: 26387/clusterfuzz-testcase-minimized-ffmpeg_dem_AVS2_fuzzer-5684222226071552

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavformat/bethsoftvid.c

@@ -28,6 +28,7 @@
  */
 
 #include "libavutil/channel_layout.h"
+#include "libavutil/imgutils.h"
 #include "libavutil/intreadwrite.h"
 #include "avformat.h"
 #include "internal.h"
@@ -72,6 +73,7 @@ static int vid_read_header(AVFormatContext *s)
 {
     BVID_DemuxContext *vid = s->priv_data;
     AVIOContext *pb = s->pb;
+    int ret;
 
     /* load main header. Contents:
     *    bytes: 'V' 'I' 'D'
@@ -84,6 +86,10 @@ static int vid_read_header(AVFormatContext *s)
     vid->bethsoft_global_delay = avio_rl16(pb);
     avio_rl16(pb);
 
+    ret = av_image_check_size(vid->width, vid->height, 0, s);
+    if (ret < 0)
+        return ret;
+
     // wait until the first packet to create each stream
     vid->video_index = -1;
     vid->audio_index = -1;