sfdisk: save errno before calling perror

errno is saved into a local variable to avoid it getting trampled
by perror before it is checked to determine the return value.

This issue seems quite rare, but I have seen it when running sfdisk
via gksudo and using the --quiet command-line option.  From what I
can tell, this combination triggers loading of translations in perror,
which (at least on my machine) ends up changing the value of errno.

Signed-off-by: Forest Bond <forest@alittletooquiet.net>

fdisk/sfdisk.c

@@ -784,10 +784,13 @@ reread_ioctl(int fd) {
     errno = ENOSYS;
 #endif
     {
+	/* perror might change errno */
+	int err = errno;
+
 	perror("BLKRRPART");
 
 	/* 2.6.8 returns EIO for a zero table */
-	if (errno == EBUSY)
+	if (err == EBUSY)
 		return -1;
     }
     return 0;