Refs #6516. Fix a regression caused by [21445] 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.

mythtv/programs/mythbackend/mainserver.cpp

@@ -5881,8 +5881,8 @@ void MainServer::reconnectTimeout(void)
         !masterServerSock->readStringList(strlist) ||
         strlist.empty() || strlist[0] == "ERROR")
     {
+        masterServerSock->Unlock(); // DownRef will delete socket...
         masterServerSock->DownRef();
-        masterServerSock->Unlock();
         masterServerSock = NULL;
         if (strlist.empty())
         {