avcodec/eatgv: use av_mallocz() for frame_buffer

Fixes use of uninitialized memory
Fixes: msan_uninit-mem_7fbf6159587b_2571_ORIGIN.TGV
Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/eatgv.c

@@ -311,7 +311,7 @@ static int tgv_decode_frame(AVCodecContext *avctx,
         frame->pict_type = AV_PICTURE_TYPE_I;
 
         if (!s->frame_buffer &&
-            !(s->frame_buffer = av_malloc(s->width * s->height)))
+            !(s->frame_buffer = av_mallocz(s->width * s->height)))
             return AVERROR(ENOMEM);
 
         if (unpack(buf, buf_end, s->frame_buffer, s->avctx->width, s->avctx->height) < 0) {