avcodec/vc2enc: Clear coef_buf on allocation

Fixes: Use of uninitialized memory
Fixes: assertion failure

Reviewed-by: <atomnuker>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit 6d00905f81)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/vc2enc.c

@@ -1088,7 +1088,7 @@ static av_cold int vc2_encode_init(AVCodecContext *avctx)
         p->dwt_width  = w = FFALIGN(p->width,  (1 << s->wavelet_depth));
         p->dwt_height = h = FFALIGN(p->height, (1 << s->wavelet_depth));
         p->coef_stride = FFALIGN(p->dwt_width, 32);
-        p->coef_buf = av_malloc(p->coef_stride*p->dwt_height*sizeof(dwtcoef));
+        p->coef_buf = av_mallocz(p->coef_stride*p->dwt_height*sizeof(dwtcoef));
         if (!p->coef_buf)
             goto alloc_fail;
         for (level = s->wavelet_depth-1; level >= 0; level--) {