mmvideo/mm_decode_intra: check horizontal coordinate too

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/mmvideo.c

@@ -104,6 +104,9 @@ static int mm_decode_intra(MmContext * s, int half_horiz, int half_vert)
         if (half_horiz)
             run_length *=2;
 
+        if (run_length > s->avctx->width - x)
+            return AVERROR_INVALIDDATA;
+
         if (color) {
             memset(s->frame.data[0] + y*s->frame.linesize[0] + x, color, run_length);
             if (half_vert)