av_strtok calls strspn on a non-NULL *saveptr, so not NULL initializing
it is an issue.
Fixes CID #1428568
Reviewed-by: Karthick Jeyapal <kjeyapal@akamai.com>
Signed-off-by: Steven Liu <lq@onvideo.cn>
Signed-off-by: Steven Liu <lq@chinaffmpeg.org>