fix generation of an url to an absolute ocs route when NC in subfolder

Signed-off-by: Arthur Schiwon <blizzz@arthur-schiwon.de>

lib/private/URLGenerator.php

@@ -94,8 +94,9 @@ class URLGenerator implements IURLGenerator {
 	public function linkToOCSRouteAbsolute(string $routeName, array $arguments = []): string {
 		$route = \OC::$server->getRouter()->generate('ocs.'.$routeName, $arguments, false);
 
-		if (strpos($route, '/index.php') === 0) {
-			$route = substr($route, 10);
+		$indexPhpPos = strpos($route, '/index.php/');
+		if ($indexPhpPos !== false) {
+			$route = substr($route, $indexPhpPos + 10);
 		}
 
 		$route = substr($route, 7);