Fixes: out of array write
Fixes: 64407/clusterfuzz-testcase-minimized-ffmpeg_BSF_H264_MP4TOANNEXB_fuzzer-4966763443650560

mp4toannexb_filter counts the number of bytes needed in the first
pass and allocate the memory, then do memcpy in the second pass.
Update sps/pps size in the loop makes the count invalid in the
case of SPS/PPS occur after IDR slice. This patch process in-band
SPS/PPS before the two pass loops.
Signed-off-by: Zhao Zhili <zhilizhao@tencent.com>