fix: don't try to setup for a user when setting up /

Signed-off-by: Robin Appelman <robin@icewind.nl>

Author: icewind1991

lib/private/Files/SetupManager.php

@@ -434,8 +434,10 @@ public function setupRoot(): void {
 	 * @param string $path
 	 * @return IUser|null
 	 */
-	private function getUserForPath(string $path) {
-		if (str_starts_with($path, '/__groupfolders')) {
+	private function getUserForPath(string $path): ?IUser {
+		if ($path === '' || $path === '/') {
+			return null;
+		} elseif (str_starts_with($path, '/__groupfolders')) {
 			return null;
 		} elseif (substr_count($path, '/') < 2) {
 			if ($user = $this->userSession->getUser()) {