close-button fix for macosx

src/gui/qt/joinnetworkgamedialog/joinnetworkgamedialogimpl.cpp

@@ -29,7 +29,8 @@ joinNetworkGameDialogImpl::joinNetworkGameDialogImpl(QWidget *parent, ConfigFile
       : QDialog(parent), myConfig(c)
 {
 
-    	
+    	setWindowModality(Qt::ApplicationModal);
+	setWindowFlags(Qt::WindowSystemMenuHint | Qt::CustomizeWindowHint | Qt::Dialog);
 	setupUi(this);
 
 // 	QShortcut *connectKey = new QShortcut(QKeySequence(Qt::Key_Enter), this);