h264: set unused ref_counts to 0 as a precautionary meassure.

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
(cherry picked from commit 3af2de76ac)

libavcodec/h264.c

@@ -2901,7 +2901,7 @@ static int decode_slice_header(H264Context *h, H264Context *h0){
         else
             h->list_count= 1;
     }else
-        h->list_count= 0;
+        h->ref_count[1]= h->ref_count[0]= h->list_count= 0;
 
     if(!default_ref_list_done){
         ff_h264_fill_default_ref_list(h);