avcodec/mpeg4videodec: Check for multiple VOL headers

Fixes multiple: runtime error: signed integer overflow: 2147115008 + 413696 cannot be represented in type 'int'
Fixes: 1723/clusterfuzz-testcase-minimized-5309409372667904
Fixes: 1727/clusterfuzz-testcase-minimized-5900685306494976
Fixes: 1737/clusterfuzz-testcase-minimized-5922321338466304

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

libavcodec/mpeg4videodec.c

@@ -2566,6 +2566,7 @@ int ff_mpeg4_decode_picture_header(Mpeg4DecContext *ctx, GetBitContext *gb)
     MpegEncContext *s = &ctx->m;
     unsigned startcode, v;
     int ret;
+    int vol = 0;
 
     /* search next start code */
     align_get_bits(gb);
@@ -2654,6 +2655,11 @@ int ff_mpeg4_decode_picture_header(Mpeg4DecContext *ctx, GetBitContext *gb)
         }
 
         if (startcode >= 0x120 && startcode <= 0x12F) {
+            if (vol) {
+                av_log(s->avctx, AV_LOG_ERROR, "Multiple VOL headers");
+                return AVERROR_INVALIDDATA;
+            }
+            vol++;
             if ((ret = decode_vol_header(ctx, gb)) < 0)
                 return ret;
         } else if (startcode == USER_DATA_STARTCODE) {