avformat/demux: Use unsigned to check duration vs duration_text

Fixes: signed integer overflow: 9223371898743775808 - -138111000000 cannot be represented in type 'long'
Fixes: 46245/clusterfuzz-testcase-minimized-ffmpeg_dem_OGG_fuzzer-5075129786302464

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

libavformat/demux.c

@@ -1612,7 +1612,7 @@ static void update_stream_timings(AVFormatContext *ic)
     else if (end_time < end_time_text)
         av_log(ic, AV_LOG_VERBOSE, "Ignoring outlier non primary stream endtime %f\n", end_time_text / (float)AV_TIME_BASE);
 
-     if (duration == INT64_MIN || (duration < duration_text && duration_text - duration < AV_TIME_BASE))
+     if (duration == INT64_MIN || (duration < duration_text && (uint64_t)duration_text - duration < AV_TIME_BASE))
          duration = duration_text;
      else if (duration < duration_text)
          av_log(ic, AV_LOG_VERBOSE, "Ignoring outlier non primary stream duration %f\n", duration_text / (float)AV_TIME_BASE);