h263: make default color black, like flv

Fixes Ticket126
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/mpegvideo.c

@@ -1134,7 +1134,7 @@ int MPV_frame_start(MpegEncContext *s, AVCodecContext *avctx)
             if(ff_alloc_picture(s, s->last_picture_ptr, 0) < 0)
                 return -1;
 
-            if(s->codec_id == CODEC_ID_FLV1){
+            if(s->codec_id == CODEC_ID_FLV1 || s->codec_id == CODEC_ID_H263){
                 for(i=0; i<s->height; i++)
                     memset(s->last_picture_ptr->f.data[0] + s->last_picture_ptr->f.linesize[0]*i, 16, s->width);
             }