Fix for ticket #1559
sh_no_output_of_prior_pics_flag is unconditionally overridden here.
According to Spec this allowed (but not mandatory) only if one of critical parameters has changed: PicWidthMaxInSamplesY, PicHeightMaxInSamplesY, MaxChromaFormat, MaxBitDepthMinus8, or dpb_max_dec_pic_buffering_minus1.