vcodec/rv34: use av_mallocz() to allocate tables

Fixes use of uninitialized memory
Fixes: msan_uninit-mem_7f75e2a55b88_4146_brokenaudio.rmvb
Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/rv34.c

@@ -1362,11 +1362,11 @@ static int rv34_decoder_alloc(RV34DecContext *r)
 {
     r->intra_types_stride = r->s.mb_width * 4 + 4;
 
-    r->cbp_chroma       = av_malloc(r->s.mb_stride * r->s.mb_height *
+    r->cbp_chroma       = av_mallocz(r->s.mb_stride * r->s.mb_height *
                                     sizeof(*r->cbp_chroma));
-    r->cbp_luma         = av_malloc(r->s.mb_stride * r->s.mb_height *
+    r->cbp_luma         = av_mallocz(r->s.mb_stride * r->s.mb_height *
                                     sizeof(*r->cbp_luma));
-    r->deblock_coefs    = av_malloc(r->s.mb_stride * r->s.mb_height *
+    r->deblock_coefs    = av_mallocz(r->s.mb_stride * r->s.mb_height *
                                     sizeof(*r->deblock_coefs));
     r->intra_types_hist = av_malloc(r->intra_types_stride * 4 * 2 *
                                     sizeof(*r->intra_types_hist));