Do not print a useless error number if mov header reading fails.

The error string is printed by ffmpeg as for other demuxers.
doc/ffmpeg: Try to clarify that the input option -r is not the same as -framerate.
fate: Fix ffprobe tests with --target-path set.
Merge remote-tracking branch 'cehoyos/master'

* cehoyos/master:
  fate: Fix ffprobe tests with --target-path set.
  doc/ffmpeg: Try to clarify that the input option -r is not the same as -framerate.
  Do not print a useless error number if mov header reading fails.

Merged-by: Michael Niedermayer <michaelni@gmx.at>