macOS: If a sheet is being shown, ignore quit and bring window to front

Otherwise, the 'exiting with an active tunnel' alert could get queued up
to be shown after the current sheet is dismissed.

WireGuard/WireGuard/UI/macOS/AppDelegate.swift

@@ -44,6 +44,11 @@ class AppDelegate: NSObject, NSApplicationDelegate {
     }
 
     @objc func quit() {
+        if let manageWindow = manageTunnelsWindowObject, manageWindow.attachedSheet != nil {
+            NSApp.activate(ignoringOtherApps: true)
+            manageWindow.orderFront(self)
+            return
+        }
         registerLoginItem(shouldLaunchAtLogin: false)
         guard let currentTunnel = tunnelsTracker?.currentTunnel, currentTunnel.status == .active || currentTunnel.status == .activating else {
             NSApp.terminate(nil)