cmd/tailscale/main: apply custom control server on first start (#156)

Currently the custom control server is not applied on start. To remedy
this, check the stored preference and if they differ issue an event to
switch to the correct backend server.

Updates: tailscale/tailscale#17470

Signed-off-by: Moritz Poldrack <git@moritz.sh>

cmd/tailscale/main.go

@@ -1302,6 +1302,11 @@ func (a *App) processUIEvents(w *app.Window, events []UIEvent, act jni.Object, s
 			a.signOut()
 			requestBackend(e)
 		case ConnectEvent:
+			if srv, _ := a.store.ReadString(customLoginServerPrefKey, ""); srv != state.backend.Prefs.ControlURL {
+				requestBackend(SetLoginServerEvent{URL: srv})
+				// wait a moment for the backend to restart
+				<-time.After(200 * time.Millisecond)
+			}
 			requestBackend(e)
 		case RouteAllEvent:
 			requestBackend(e)