UI: fix crash due to NULL dereference

UI/window-basic-main.cpp

@@ -6830,7 +6830,7 @@ void OBSBasic::IconActivated(QSystemTrayIcon::ActivationReason reason)
 void OBSBasic::SysTrayNotify(const QString &text,
 		QSystemTrayIcon::MessageIcon n)
 {
-	if (QSystemTrayIcon::supportsMessages()) {
+	if (trayIcon && QSystemTrayIcon::supportsMessages()) {
 		QSystemTrayIcon::MessageIcon icon =
 				QSystemTrayIcon::MessageIcon(n);
 		trayIcon->showMessage("OBS Studio", text, icon, 10000);