error_concealment: Prevent FPEs in case of corrupted input.

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/error_resilience.c

@@ -248,7 +248,7 @@ static void guess_dc(MpegEncContext *s, int16_t *dc, int w,
             weight_sum = 0;
             guess      = 0;
             for (j = 0; j < 4; j++) {
-                int64_t weight  = 256 * 256 * 256 * 16 / dist[b_x + b_y*stride][j];
+                int64_t weight  = 256 * 256 * 256 * 16 / FFMAX(dist[b_x + b_y*stride][j], 1);
                 guess          += weight*(int64_t)col[b_x + b_y*stride][j];
                 weight_sum     += weight;
             }