error_conceal: fix FPE in guess_dc() with huge sizes.

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/error_resilience.c

@@ -174,7 +174,7 @@ static void guess_dc(MpegEncContext *s, int16_t *dc, int w,
 {
     int b_x, b_y;
     int16_t  (*col )[4] = av_malloc(stride*h*sizeof( int16_t)*4);
-    uint16_t (*dist)[4] = av_malloc(stride*h*sizeof(uint16_t)*4);
+    uint32_t (*dist)[4] = av_malloc(stride*h*sizeof(uint32_t)*4);
 
     for(b_y=0; b_y<h; b_y++){
         int color= 1024;