v410enc: fix output buffer size check

The encoder clearly needs width * height * 4 bytes.
Signed-off-by: Mans Rullgard <mans@mansr.com>

libavcodec/v410enc.c

@@ -50,7 +50,7 @@ static int v410_encode_frame(AVCodecContext *avctx, uint8_t *buf,
     int i, j;
     int output_size = 0;
 
-    if (buf_size < avctx->width * avctx->height * 3) {
+    if (buf_size < avctx->width * avctx->height * 4) {
         av_log(avctx, AV_LOG_ERROR, "Out buffer is too small.\n");
         return AVERROR(ENOMEM);
     }