set base url for urlhelper early in jsonapi.php (and remove some clutter), fixes #4712

Closes #4712

Merge request studip/studip!3505

public/jsonapi.php

 <?php
 
-use DI\ContainerBuilder;
 use Slim\Factory\AppFactory;
 
 require '../lib/bootstrap.php';
-require '../composer/autoload.php';
 
 \StudipAutoloader::addAutoloadPath($GLOBALS['STUDIP_BASE_PATH'] . DIRECTORY_SEPARATOR . 'vendor/oauth-php/library/');
 
+// Set base url for URLHelper class
+URLHelper::setBaseUrl($GLOBALS['CANONICAL_RELATIVE_PATH_STUDIP']);
+
 page_open([
     'sess' => 'Seminar_Session',
     'auth' => 'Seminar_Default_Auth',
@@ -15,9 +16,6 @@ page_open([
     'user' => 'Seminar_User',
 ]);
 
-// Set base url for URLHelper class
-URLHelper::setBaseUrl($GLOBALS['CANONICAL_RELATIVE_PATH_STUDIP']);
-
 // Instantiate the app
 $container = app();
 AppFactory::setContainer($container);