Auth/PublicArea: Fix auto SSO for SOAP and Apache authentication

With 871004d the `cmd=force_login`
parameter will always be used if a server request results in the
presentation of the login page. So everytime the login page is
displayed, this parameter is set, even if the `Public Area`
is disabled.
Because of this, the automatic login attempts for `SOAP` and
`Apache` authentication (`ilStartUpGUI::showLoginPage`) do not work
anymore.
This change introduces a further check before
`ilInitialisation::redirectToStartingPage` is called. Without this
change `// fallback, should never happen` in
`ilInitialisation::redirectToStartingPage` does always happen.

Services/Init/classes/class.ilStartUpGUI.php

@@ -1556,8 +1556,12 @@ protected function processIndexPHP(): void
 
         // In case of an valid session, redirect to starting page
         if ($this->authSession->isValid()) {
-            ilInitialisation::redirectToStartingPage();
-            return;
+            if (!$this->user->isAnonymous() || ilPublicSectionSettings::getInstance()->isEnabledForDomain(
+                $this->httpRequest->getServerParams()['SERVER_NAME']
+            )) {
+                ilInitialisation::redirectToStartingPage();
+                return;
+            }
         }
 
         if (ilPublicSectionSettings::getInstance()->isEnabledForDomain($_SERVER['SERVER_NAME'])) {