SMPP: fix possible NULL pointer dereference

Related: OS#5568
Change-Id: I875eb5249004d3a960aee46c5099592d18fcaa76
diff --git a/src/libsmpputil/smpp_smsc.c b/src/libsmpputil/smpp_smsc.c
index 059915d..0ee5b62 100644
--- a/src/libsmpputil/smpp_smsc.c
+++ b/src/libsmpputil/smpp_smsc.c
@@ -163,8 +163,8 @@
 		osmo_fd_unregister(&esme->wqueue.bfd);
 		close(esme->wqueue.bfd.fd);
 		esme->wqueue.bfd.fd = -1;
-		acl->esme = NULL;
 		smpp_esme_put(acl->esme);
+		acl->esme = NULL;
 	}
 
 	/* delete all routes for this ACL */