Merge pull request #29000 from nextcloud/backport/28995/stable20

[stable20] Fix redirect during initial setup

lib/private/URLGenerator.php

@@ -271,7 +271,8 @@ public function linkToDocs(string $key): string {
 	 * @return string base url of the current request
 	 */
 	public function getBaseUrl(): string {
-		if ($this->baseUrl === null) {
+		// BaseUrl can be equal to 'http(s)://' during the first steps of the intial setup.
+		if ($this->baseUrl === null || $this->baseUrl === "http://" || $this->baseUrl === "https://") {
 			$this->baseUrl = $this->request->getServerProtocol() . '://' . $this->request->getServerHost() . \OC::$WEBROOT;
 		}
 		return $this->baseUrl;