mpegvideo_enc/rv20: width and height must be multiple of 4

RealPlayer does not play rv20 files when sizes are not multiple of 4
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/mpegvideo_enc.c

@@ -561,6 +561,13 @@ av_cold int ff_MPV_encode_init(AVCodecContext *avctx)
         return AVERROR(EINVAL);
     }
 
+    if (s->codec_id == AV_CODEC_ID_RV20 &&
+        (avctx->width &3 ||
+         avctx->height&3 )) {
+        av_log(avctx, AV_LOG_ERROR, "width and height must be a multiple of 4\n");
+        return AVERROR(EINVAL);
+    }
+
     if ((s->codec_id == AV_CODEC_ID_WMV1 ||
          s->codec_id == AV_CODEC_ID_WMV2) &&
          avctx->width & 1) {