Close register-page before opening login-page

The `onTick` of the register-page was still running when connecting to
the lobby. This lead to an error when the `connect` message was
received.
With this commit returning from the login-page will always return to the
entrance-page. Previously it returned to the register-page when it was
opened by through that page.

binaries/data/mods/public/gui/prelobby/common/feedback/feedback.js

@@ -42,4 +42,6 @@ async function cancelButton()
 	await new Promise(resolve => { Engine.GetGUIObjectByName("cancel").onPress = resolve; });
 	if (Engine.HasXmppClient())
 		Engine.StopXmppClient();
+
+	return false;
 }

binaries/data/mods/public/gui/prelobby/entrance/entrance.js

@@ -13,7 +13,8 @@ function loginButton()
 	Engine.OpenChildPage("page_prelobby_login.xml");
 }
 
-function registerButton()
+async function registerButton()
 {
-	Engine.OpenChildPage("page_prelobby_register.xml");
+	if (await Engine.OpenChildPage("page_prelobby_register.xml"))
+		Engine.OpenChildPage("page_prelobby_login.xml");
 }

binaries/data/mods/public/gui/prelobby/register/register.js

@@ -40,6 +40,5 @@ async function onRegistered()
 	setFeedback(translate("Registered"));
 
 	Engine.StopXmppClient();
-
-	Engine.OpenChildPage("page_prelobby_login.xml");
+	return true;
 }