Merge #14228: Qt: Enable system tray icon by default if available

ec1201a368 Don't use systray icon on inappropriate systems (Hennadii Stepanov)

Pull request description:

  Prevent a user from losing access to the main window by minimizing it to the tray on the systems which have not “system tray” or “notification area” available (e.g. GNOME 3.26+).

  Tested on Fedora 28 + GNOME 3.28.

Tree-SHA512: c2dc26ff31c38a882dbd7d1ff71af99f1ba38a04a1c8b7fe7b99b93e4c0719f2916c7db0e620806a36582402d18939c635e1913c276b452ecbf939936067407b

src/qt/bitcoingui.cpp

@@ -127,7 +127,9 @@ BitcoinGUI::BitcoinGUI(interfaces::Node& node, const PlatformStyle *_platformSty
     createToolBars();
 
     // Create system tray icon and notification
-    createTrayIcon(networkStyle);
+    if (QSystemTrayIcon::isSystemTrayAvailable()) {
+        createTrayIcon(networkStyle);
+    }
 
     // Create status bar
     statusBar();
@@ -588,6 +590,8 @@ void BitcoinGUI::setWalletActionsEnabled(bool enabled)
 
 void BitcoinGUI::createTrayIcon(const NetworkStyle *networkStyle)
 {
+    assert(QSystemTrayIcon::isSystemTrayAvailable());
+
 #ifndef Q_OS_MAC
     trayIcon = new QSystemTrayIcon(this);
     QString toolTip = tr("%1 client").arg(tr(PACKAGE_NAME)) + " " + networkStyle->getTitleAddText();