avformat/cafdec: dont seek beyond 64bit

Fixes: signed integer overflow: 64 + 9223372036854775807 cannot be represented in type 'long long'
Fixes: 51896/clusterfuzz-testcase-minimized-ffmpeg_dem_CAF_fuzzer-6418242730328064
Fixes: 62276/clusterfuzz-testcase-minimized-ffmpeg_dem_CAF_fuzzer-6418242730328064

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

libavformat/cafdec.c

@@ -271,7 +271,7 @@ static int read_pakt_chunk(AVFormatContext *s, int64_t size)
         }
     }
 
-    if (avio_tell(pb) - ccount > size) {
+    if (avio_tell(pb) - ccount > size || size > INT64_MAX - ccount) {
         av_log(s, AV_LOG_ERROR, "error reading packet table\n");
         return AVERROR_INVALIDDATA;
     }