avcodec/dxa: check dimensions

Fixes out of array access
Fixes: asan_heap-oob_11222fb_21_020.dxa
Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/dxa.c

@@ -329,6 +329,11 @@ static av_cold int decode_init(AVCodecContext *avctx)
 {
     DxaDecContext * const c = avctx->priv_data;
 
+    if (avctx->width%4 || avctx->height%4) {
+        avpriv_request_sample(avctx, "dimensions are not a multiple of 4");
+        return AVERROR_INVALIDDATA;
+    }
+
     c->prev = av_frame_alloc();
     if (!c->prev)
         return AVERROR(ENOMEM);