avformat/jacosubdec: Fix timeres to 1/100 units convertion overflow

Fixes: signed integer overflow: 44444442 * 100 cannot be represented in type 'int'
Fixes: 15117/clusterfuzz-testcase-minimized-ffmpeg_DEMUXER_fuzzer-5164660531134464

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

libavformat/jacosubdec.c

@@ -107,6 +107,7 @@ static const char *read_ts(JACOsubContext *jacosub, const char *buf,
     unsigned hs, ms, ss, fs; // hours, minutes, seconds, frame start
     unsigned he, me, se, fe; // hours, minutes, seconds, frame end
     int ts_start, ts_end;
+    int64_t ts_start64, ts_end64;
 
     /* timed format */
     if (sscanf(buf, "%u:%u:%u.%u %u:%u:%u.%u %n",
@@ -124,10 +125,10 @@ static const char *read_ts(JACOsubContext *jacosub, const char *buf,
     return NULL;
 
 shift_and_ret:
-    ts_start  = (ts_start + jacosub->shift) * 100 / jacosub->timeres;
-    ts_end    = (ts_end   + jacosub->shift) * 100 / jacosub->timeres;
-    *start    = ts_start;
-    *duration = ts_end - ts_start;
+    ts_start64  = (ts_start + jacosub->shift) * 100LL / jacosub->timeres;
+    ts_end64    = (ts_end   + jacosub->shift) * 100LL / jacosub->timeres;
+    *start    = ts_start64;
+    *duration = ts_end64 - ts_start64;
     return buf + len;
 }