Avoid crash when file transfer can't open files

916e43b inadvertently adds a failed File Transfer to the fileTransferList
causing a segfault when a subsequent socket disconnection attempts to clean up and
delete the File Transfer again.

Fixes #12650

mythtv/programs/mythbackend/mainserver.cpp

@@ -1941,15 +1941,13 @@ void MainServer::HandleAnnounce(QStringList &slist, QStringList commands,
             if (!controlSocketList.remove(socket))
                 return; // socket was disconnected
             ft = new FileTransfer(filename, socket, writemode);
-            fileTransferList.push_back(ft);
         }
         else
         {
             QWriteLocker lock(&sockListLock);
             if (!controlSocketList.remove(socket))
                 return; // socket was disconnected
             ft = new FileTransfer(filename, socket, usereadahead, timeout_ms);
-            fileTransferList.push_back(ft);
         }
 
         if (!ft->isOpen())
@@ -1963,6 +1961,7 @@ void MainServer::HandleAnnounce(QStringList &slist, QStringList commands,
             return;
         }
         ft->IncrRef();
+        fileTransferList.push_back(ft);
 
         retlist << QString::number(socket->GetSocketDescriptor());
         retlist << QString::number(ft->GetFileSize());