smacker: fix off-by-one error in palette expanding code

libavformat/smacker.c

@@ -274,7 +274,7 @@ static int smacker_read_packet(AVFormatContext *s, AVPacket *pkt)
                 } else if(t & 0x40){ /* copy with offset */
                     off = avio_r8(s->pb);
                     j = (t & 0x3F) + 1;
-                    if (off + j > 0xff) {
+                    if (off + j > 0x100) {
                         av_log(s, AV_LOG_ERROR,
                                "Invalid palette update, offset=%d length=%d extends beyond palette size\n",
                                off, j);