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>
(cherry picked from commit e70312dfc2)

Conflicts:

	libavcodec/dxa.c

libavcodec/dxa.c

@@ -308,6 +308,11 @@ static av_cold int decode_init(AVCodecContext *avctx)
 
     avctx->pix_fmt = AV_PIX_FMT_PAL8;
 
+    if (avctx->width%4 || avctx->height%4) {
+        av_log(avctx, AV_LOG_ERROR, "dimensions are not a multiple of 4");
+        return AVERROR_INVALIDDATA;
+    }
+
     avcodec_get_frame_defaults(&c->pic);
     avcodec_get_frame_defaults(&c->prev);