tm2dec: fix overread

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/truemotion2.c

@@ -272,7 +272,7 @@ static int tm2_read_stream(TM2Context *ctx, const uint8_t *buf, int stream_id, i
     if(len == 0)
         return 4;
 
-    if (len >= INT_MAX/4-1 || len < 0 || len > buf_size) {
+    if (len >= INT_MAX/4-1 || len < 0 || skip > buf_size) {
         av_log(ctx->avctx, AV_LOG_ERROR, "Error, invalid stream size.\n");
         return -1;
     }