[FFmpeg-cvslog] avformat/utils: Check timebase before use in estimate_timings()

ffmpeg | branch: release/4.1 | Michael Niedermayer | Sat Jun 29 23:23:25 2019 +0200| [a1416c6c8d1234a53b7e52f45d7f5d613ff8cf10] | committer: Michael Niedermayer avformat/utils: Check timebase before use in estimate_timings() Fixes: division by 0 Fixes: 15480/clusterfuzz-testcase-minimized-ffm

[FFmpeg-cvslog] avformat/utils: Check timebase before use in estimate_timings()

ffmpeg | branch: master | Michael Niedermayer | Sat Jun 29 23:23:25 2019 +0200| [f57e97dfd9539bc3f4f97a76ebc001f0b055cb88] | committer: Michael Niedermayer avformat/utils: Check timebase before use in estimate_timings() Fixes: division by 0 Fixes: 15480/clusterfuzz-testcase-minimized-ffmpeg_D