error_resilience: actually add counter when adding a MV predictor.

Without, the predictor isn't actually used.

libavcodec/error_resilience.c

@@ -547,6 +547,7 @@ skip_mean_and_median:
                     mv_predictor[pred_count][0]= prev_x;
                     mv_predictor[pred_count][1]= prev_y;
                     ref         [pred_count]   = prev_ref;
+                    pred_count++;
 
                     s->mv_dir = MV_DIR_FORWARD;
                     s->mb_intra=0;

tests/ref/vsynth1/error

 7416dfd319f04044d4575dc9d1b406e1 *./tests/data/vsynth1/error-mpeg4-adv.avi
   756836 ./tests/data/vsynth1/error-mpeg4-adv.avi
-54342963593ba08bcde95244a011efe5 *./tests/data/error.vsynth1.out.yuv
-stddev:   17.59 PSNR: 23.22 MAXDIFF:  240 bytes:  7603200/  7603200
+79e94ba32b37759397362cbcb479d4d3 *./tests/data/error.vsynth1.out.yuv
+stddev:   18.36 PSNR: 22.85 MAXDIFF:  243 bytes:  7603200/  7603200

tests/ref/vsynth2/error

 90e65096aa9ebafa3fe3f44a5a47cdc4 *./tests/data/vsynth2/error-mpeg4-adv.avi
   176588 ./tests/data/vsynth2/error-mpeg4-adv.avi
-ce12aa852126f2740838dd2da9e21a03 *./tests/data/error.vsynth2.out.yuv
-stddev:   10.06 PSNR: 28.08 MAXDIFF:  193 bytes:  7603200/  7603200
+96baa9e4c24c837a3ba5abd8dd2cdd30 *./tests/data/error.vsynth2.out.yuv
+stddev:    8.98 PSNR: 29.06 MAXDIFF:  184 bytes:  7603200/  7603200