Silence compiler warnings for XL decoder

Originally committed as revision 16921 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/xl.c

@@ -48,7 +48,7 @@ static int decode_frame(AVCodecContext *avctx,
     int i, j;
     int stride;
     uint32_t val;
-    int y0, y1, y2, y3, c0, c1;
+    int y0, y1, y2, y3 = 0, c0 = 0, c1 = 0;
 
     if(p->data[0])
         avctx->release_buffer(avctx, p);