avcodec/mpeg4videodec: Check also for negative versions in the validity check

Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit 0e7865ce)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/mpeg4videodec.c

@@ -2137,7 +2137,7 @@ static int decode_user_data(Mpeg4DecContext *ctx, GetBitContext *gb)
     if (e != 4) {
         e = sscanf(buf, "Lavc%d.%d.%d", &ver, &ver2, &ver3) + 1;
         if (e > 1) {
-            if (ver > 0xFF || ver2 > 0xFF || ver3 > 0xFF) {
+            if (ver > 0xFFU || ver2 > 0xFFU || ver3 > 0xFFU) {
                 av_log(s->avctx, AV_LOG_WARNING,
                      "Unknown Lavc version string encountered, %d.%d.%d; "
                      "clamping sub-version values to 8-bits.\n",