[Qt] disable tray interactions when client model set to 0

- this prevents the ability to fiddle around with the system tray when
  already shutting down (e.g. on slow shutdowns because of a proxy delay)
- extends solution for #4360

src/qt/bitcoingui.cpp

@@ -89,6 +89,7 @@ BitcoinGUI::BitcoinGUI(bool fIsTestnet, QWidget *parent) :
     openAction(0),
     showHelpMessageAction(0),
     trayIcon(0),
+    trayIconMenu(0),
     notificator(0),
     rpcConsole(0),
     prevBlocks(0),
@@ -449,8 +450,12 @@ void BitcoinGUI::setClientModel(ClientModel *clientModel)
             walletFrame->setClientModel(clientModel);
         }
 #endif
-
+        unitDisplayControl->setOptionsModel(clientModel->getOptionsModel());
-        this->unitDisplayControl->setOptionsModel(clientModel->getOptionsModel());
+    } else {
+        // Disable possibility to show main window via action
+        toggleHideAction->setEnabled(false);
+        // Disable context menu on tray icon
+        trayIconMenu->clear();
     }
 }
 
@@ -519,7 +524,6 @@ void BitcoinGUI::createTrayIcon(bool fIsTestnet)
 
 void BitcoinGUI::createTrayIconMenu()
 {
-    QMenu *trayIconMenu;
 #ifndef Q_OS_MAC
     // return if trayIcon is unset (only on non-Mac OSes)
     if (!trayIcon)
@@ -560,7 +564,7 @@ void BitcoinGUI::trayIconActivated(QSystemTrayIcon::ActivationReason reason)
     if(reason == QSystemTrayIcon::Trigger)
     {
         // Click on system tray icon triggers show/hide of the main window
-        toggleHideAction->trigger();
+        toggleHidden();
     }
 }
 #endif
@@ -946,6 +950,7 @@ void BitcoinGUI::showNormalIfMinimized(bool fToggleHidden)
 {
     if(!clientModel)
         return;
+
     // activateWindow() (sometimes) helps with keyboard focus on Windows
     if (isHidden())
     {

src/qt/bitcoingui.h

@@ -103,6 +103,7 @@ private:
     QAction *showHelpMessageAction;
 
     QSystemTrayIcon *trayIcon;
+    QMenu *trayIconMenu;
     Notificator *notificator;
     RPCConsole *rpcConsole;