avformat/jacosubdec: Use 64bit for abs

Fixes: negation of -2147483648 cannot be represented in type 'int'; cast to an unsigned type to negate this value to itself
Fixes: 62276/clusterfuzz-testcase-minimized-ffmpeg_dem_JACOSUB_fuzzer-5401294942371840

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

libavformat/jacosubdec.c

@@ -150,7 +150,7 @@ static int get_shift(unsigned timeres, const char *buf)
     }
 
     ret = (int64_t)h*3600 + (int64_t)m*60 + s;
-    if (FFABS(ret) > (INT64_MAX - FFABS(d)) / timeres)
+    if (FFABS(ret) > (INT64_MAX - FFABS((int64_t)d)) / timeres)
         return 0;
     ret = sign * (ret * timeres + d);