when set option fmp4_init_filename to init_%v.mp4
before patch:
the init file will be init_%v_0.mp4, init_%v_1.mp4
after patch:
the init file will be init_0.mp4, init_1.mp4
Reported-By: Gyan Doshi <ffmpeg@gyani.pro>
Signed-off-by: Steven Liu <lq@chinaffmpeg.org>