Refs #6516. Fix a regression caused by  aka [2fdeb3f].
We were unlocking a mutex after it was deleted. The lock is for the writeStringList()/readStringList() and should have been released before the DownRef(). Thanks go to Helen Buus for finding this.
|@@ -5881,8 +5881,8 @@ void MainServer::reconnectTimeout(void)|
|strlist.empty() || strlist == "ERROR")|
|+ masterServerSock->Unlock(); // DownRef will delete socket...|
|masterServerSock = NULL;|