Fix the problem discussed here :
https://github.com/jitsi/libjitsi/pull/11#issuecomment-49404492
Also fix a bug where the first frame only was send (when loopFile was true) :

FFmpeg doesn't set the number of frame contained in the IVF file, so
the IVFFileReader was reading only the first frame because it thought
it has reached the last frame. It now use the EOF to know if the end
is reached or not.