libext2fs: fix uninitialized length in rep_strdup()

For platforms whose libc don't supply strdup(), the replacement strdup
function in lib/ext2fs/tdb.c needs to always initialize the length
variable.

Reported-by: Vladyslav Tsilytskyi <ykp@protonmail.ch>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
diff --git a/lib/ext2fs/tdb.c b/lib/ext2fs/tdb.c
index 195a4c0..5091b12 100644
--- a/lib/ext2fs/tdb.c
+++ b/lib/ext2fs/tdb.c
@@ -79,12 +79,10 @@
 {
 	char *ret;
 	int length;
+
 	if (!s)
 		return NULL;
-
-	if (!length)
-		length = strlen(s);
-
+	length = strlen(s);
 	ret = malloc(length + 1);
 	if (ret) {
 		strncpy(ret, s, length);