media: mediatek: vcodec: Fix getting NULL pointer for dst buffer

The driver may can't get v4l2 buffer when lat or core decode timeout,
will lead to crash when call v4l2_m2m_buf_done to set dst buffer
(NULL pointer) done.

Fixes: 7b182b8d ("media: mediatek: vcodec: Refactor get and put capture buffer flow")
Signed-off-by: Yunfei Dong <yunfei.dong@mediatek.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>

drivers/media/platform/mediatek/vcodec/mtk_vcodec_dec_stateless.c

@@ -138,10 +138,13 @@ static void mtk_vdec_stateless_cap_to_disp(struct mtk_vcodec_ctx *ctx, int error
 		state = VB2_BUF_STATE_DONE;
 
 	vb2_dst = v4l2_m2m_dst_buf_remove(ctx->m2m_ctx);
-	v4l2_m2m_buf_done(vb2_dst, state);
-
-	mtk_v4l2_debug(2, "free frame buffer id:%d to done list",
-		       vb2_dst->vb2_buf.index);
+	if (vb2_dst) {
+		v4l2_m2m_buf_done(vb2_dst, state);
+		mtk_v4l2_debug(2, "free frame buffer id:%d to done list",
+			       vb2_dst->vb2_buf.index);
+	} else {
+		mtk_v4l2_err("dst buffer is NULL");
+	}
 
 	if (src_buf_req)
 		v4l2_ctrl_request_complete(src_buf_req, &ctx->ctrl_hdl);