avformat/sbgdec: Fixes integer overflow in str_to_time() with hours

Fixes: signed integer overflow: 904444 * 3600 cannot be represented in type 'int'
Fixes: 15113/clusterfuzz-testcase-minimized-ffmpeg_DEMUXER_fuzzer-5764083346833408

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

libavformat/sbgdec.c

@@ -197,7 +197,7 @@ static int str_to_time(const char *str, int64_t *rtime)
         if (end > cur + 1)
             cur = end;
     }
-    *rtime = (hours * 3600 + minutes * 60 + seconds) * AV_TIME_BASE;
+    *rtime = (hours * 3600LL + minutes * 60LL + seconds) * AV_TIME_BASE;
     return cur - str;
 }