h264 - Correct implicit weight table computation for long ref pics

Correct computation of implicit weight tables when referencing pictures
that are marked for long reference.

libavcodec/h264.c

@@ -2174,9 +2174,10 @@ static void implicit_weight_table(H264Context *h, int field){
     for(ref0=ref_start; ref0 < ref_count0; ref0++){
         int poc0 = h->ref_list[0][ref0].poc;
         for(ref1=ref_start; ref1 < ref_count1; ref1++){
+            int w= 32;
+            if (!h->ref_list[0][ref0].long_ref && !h->ref_list[1][ref1].long_ref){
             int poc1 = h->ref_list[1][ref1].poc;
             int td = av_clip(poc1 - poc0, -128, 127);
-            int w= 32;
             if(td){
                 int tb = av_clip(cur_poc - poc0, -128, 127);
                 int tx = (16384 + (FFABS(td) >> 1)) / td;
@@ -2184,6 +2185,7 @@ static void implicit_weight_table(H264Context *h, int field){
                 if(dist_scale_factor >= -64 && dist_scale_factor <= 128)
                     w = 64 - dist_scale_factor;
             }
+            }
             if(field<0){
                 h->implicit_weight[ref0][ref1][0]=
                 h->implicit_weight[ref0][ref1][1]= w;