avcodec/snow: fix 1 pixel block sizes

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

libavcodec/snow.c

@@ -358,9 +358,13 @@ void ff_snow_pred_block(SnowContext *s, uint8_t *dst, uint8_t *tmp, ptrdiff_t st
 
         av_assert2(s->chroma_h_shift == s->chroma_v_shift); // only one mv_scale
 
-        av_assert2(b_w>1 && b_h>1);
         av_assert2((tab_index>=0 && tab_index<4) || b_w==32);
-        if((dx&3) || (dy&3) || !(b_w == b_h || 2*b_w == b_h || b_w == 2*b_h) || (b_w&(b_w-1)) || !s->plane[plane_index].fast_mc )
+        if(    (dx&3) || (dy&3)
+            || !(b_w == b_h || 2*b_w == b_h || b_w == 2*b_h)
+            || (b_w&(b_w-1))
+            || b_w == 1
+            || b_h == 1
+            || !s->plane[plane_index].fast_mc )
             mc_block(&s->plane[plane_index], dst, src, stride, b_w, b_h, dx, dy);
         else if(b_w==32){
             int y;