libbb: add xfstat function

function                                             old     new   delta
xfstat                                                 -      25     +25
mkfs_ext2_main                                      2421    2423      +2
mkfs_reiser_main                                    1197    1194      -3
next                                                 312     307      -5
ar_main                                              533     522     -11
mkfs_minix_main                                     2938    2924     -14
mkfs_vfat_main                                      1511    1495     -16
writeTarFile                                         272     255     -17
------------------------------------------------------------------------------
(add/remove: 1/0 grow/shrink: 1/6 up/down: 27/-66)            Total: -39 bytes

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
diff --git a/libbb/update_passwd.c b/libbb/update_passwd.c
index e050dfc..a2be0f1 100644
--- a/libbb/update_passwd.c
+++ b/libbb/update_passwd.c
@@ -133,7 +133,7 @@
 	goto close_old_fp;
 
  created:
-	if (!fstat(old_fd, &sb)) {
+	if (fstat(old_fd, &sb) == 0) {
 		fchmod(new_fd, sb.st_mode & 0777); /* ignore errors */
 		fchown(new_fd, sb.st_uid, sb.st_gid);
 	}