truemotion2: Fix the buffer check

The variable skip contains the expected size in bytes.

Bug-Id: 906
CC: libav-stable@libav.org
Signed-off-by: NLuca Barbato <lu_zero@gentoo.org>

libavcodec/truemotion2.c

@@ -291,7 +291,7 @@ 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 AVERROR_INVALIDDATA;
     }