avformat/dhav: Limit get_duration() iterations

Fixes: Timeout
Fixes: 39971/clusterfuzz-testcase-minimized-ffmpeg_IO_DEMUXER_fuzzer-5756969890217984
Fixes: 39977/clusterfuzz-testcase-minimized-ffmpeg_dem_DHAV_fuzzer-5327123053674496

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

libavformat/dhav.c

@@ -234,12 +234,13 @@ static int64_t get_duration(AVFormatContext *s)
     int64_t start_pos = avio_tell(s->pb);
     int64_t start = 0, end = 0;
     struct tm timeinfo;
+    int max_interations = 100000;
 
     if (!s->pb->seekable)
         return 0;
 
     avio_seek(s->pb, avio_size(s->pb) - 8, SEEK_SET);
-    while (avio_tell(s->pb) > 12) {
+    while (avio_tell(s->pb) > 12 && max_interations--) {
         if (avio_rl32(s->pb) == MKTAG('d','h','a','v')) {
             int seek_back = avio_rl32(s->pb);