Initialize avctx->pix_fmt in av1_parser.c
AV1 Chroma format is invalid when quering using below code if no AV1 decoder
is available:

iVideoStream = av_find_best_stream(fmtc, AVMEDIA_TYPE_VIDEO, -1, -1, NULL, 0);
eChromaFormat = (AVPixelFormat)fmtc->streams[iVideoStream]->codecpar->format;
Signed-off-by: James Almer <jamrial@gmail.com>
(cherry picked from commit 23d06f606e58779d47ca9d312c570b8e64f99f9e)