Infinite loop when reading subtitles with FFprobe

[Carl Eugen Hoyos]

​http://thread.gmane.org/gmane.comp.video.ffmpeg.user/61720
A user reported an infinite loop when using FFprobe. This is a regression since 29412821241050c846dbceaad4b9752857659977

$ ffprobe pgssub-ffprobe.infinite.loop.mpg -select_streams s:0 -show_frames -print_format flat | grep pts_time
ffprobe version N-79083-gc411e90 Copyright (c) 2007-2016 the FFmpeg developers
  built with gcc 4.8 (SUSE Linux)
  configuration: --enable-gpl
  libavutil      55. 19.100 / 55. 19.100
  libavcodec     57. 28.103 / 57. 28.103
  libavformat    57. 28.102 / 57. 28.102
  libavdevice    57.  0.101 / 57.  0.101
  libavfilter     6. 39.102 /  6. 39.102
  libswscale      4.  0.100 /  4.  0.100
  libswresample   2.  0.101 /  2.  0.101
  libpostproc    54.  0.100 / 54.  0.100
Input #0, mpeg, from 'pgssub-ffprobe.infinite.loop.mpg':
  Duration: 00:00:10.55, start: 0.541711, bitrate: 10382 kb/s
    Stream #0:0[0x1e0]: Video: mpeg2video (Main), yuv420p(tv), 1920x1080 [SAR 1:1 DAR 16:9], max. 30000 kb/s, 23.98 fps, 23.98 tbr, 90k tbn, 47.95 tbc
    Stream #0:1[0x80]: Audio: ac3, 48000 Hz, 5.1(side), fltp, 448 kb/s
    Stream #0:2[0x20]: Subtitle: dvd_subtitle
frames.subtitle.0.pts_time="2.685711"
frames.subtitle.1.pts_time="2.685711"
frames.subtitle.2.pts_time="2.685711"
frames.subtitle.3.pts_time="2.685711"
frames.subtitle.4.pts_time="2.685711"
frames.subtitle.5.pts_time="2.685711"
frames.subtitle.6.pts_time="2.685711"
frames.subtitle.7.pts_time="2.685711"
frames.subtitle.8.pts_time="2.685711"
frames.subtitle.9.pts_time="2.685711"

[Clément Bœsch]

Regression since 29412821241050c846dbceaad4b9752857659977.

Fixed in bbf02f7d288681d2ba6d522a99e6341dc3984247.