Fix for rpl_start_stop_slave failure

One may access freed THD members after LOCK_thd_kill is released.

With original code it can happen when killing wsrep-disabled thread on a
wsrep-enabled server. With 91ab42a8 it is happening on a wsrep-disabled
server.

sql/sql_parse.cc

@@ -9086,8 +9086,8 @@ kill_one_thread(THD *thd, longlong id, killed_state kill_signal, killed_type typ
     else
       error= (type == KILL_TYPE_QUERY ? ER_KILL_QUERY_DENIED_ERROR :
                                         ER_KILL_DENIED_ERROR);
-    mysql_mutex_unlock(&tmp->LOCK_thd_kill);
     if (WSREP(tmp)) mysql_mutex_unlock(&tmp->LOCK_thd_data);
+    mysql_mutex_unlock(&tmp->LOCK_thd_kill);
   }
   DBUG_PRINT("exit", ("%d", error));
   DBUG_RETURN(error);