libselinux: Fix NULL pointer use in selinux_restorecon_set_sehandle

error occur when selinux_restorecon_default_handle return NULL in
restorecon_init.

fixes: SELinuxProject/selinux#249

Signed-off-by: Ji Qin <jiqin.ji@huawei.com>
Acked-by: Stephen Smalley <stephen.smalley.work@gmail.com>

libselinux/src/selinux_restorecon.c

@@ -1154,6 +1154,8 @@ void selinux_restorecon_set_sehandle(struct selabel_handle *hndl)
 	size_t num_specfiles, fc_digest_len;
 
 	fc_sehandle = (struct selabel_handle *) hndl;
+	if (!fc_sehandle)
+		return;
 
 	/* Check if digest requested in selabel_open(3), if so use it. */
 	if (selabel_digest(fc_sehandle, &fc_digest, &fc_digest_len,