mix_parser: check idx in h264_dpb_get_smallest_poc to fix klocwork issue

BZ: 148198

check idx in h264_dpb_get_smallest_poc to fix klocwork issue

Change-Id: I96a6ed242f17d82281707822ee37cc9bda836bcc
Signed-off-by: ywan171 <yi.a.wang@intel.com>
1 file changed