Fix displayName return of dav groups request

Signed-off-by: John Molakvoæ (skjnldsv) <skjnldsv@protonmail.com>

Author: skjnldsv

apps/dav/lib/DAV/GroupPrincipalBackend.php

@@ -293,10 +293,12 @@ function findByUri($uri, $principalPrefix) {
 	 */
 	protected function groupToPrincipal($group) {
 		$groupId = $group->getGID();
+		// getDisplayName returns UID if none
+		$displayName = $group->getDisplayName();
 
 		return [
 			'uri' => 'principals/groups/' . urlencode($groupId),
-			'{DAV:}displayname' => $this->l10n->t('%s (group)', [$groupId]),
+			'{DAV:}displayname' => $displayName,
 			'{urn:ietf:params:xml:ns:caldav}calendar-user-type' => 'GROUP',
 		];
 	}
@@ -307,11 +309,12 @@ protected function groupToPrincipal($group) {
 	 */
 	protected function userToPrincipal($user) {
 		$userId = $user->getUID();
+		// getDisplayName returns UID if none
 		$displayName = $user->getDisplayName();
 
 		$principal = [
 			'uri' => 'principals/users/' . $userId,
-			'{DAV:}displayname' => is_null($displayName) ? $userId : $displayName,
+			'{DAV:}displayname' => $displayName,
 			'{urn:ietf:params:xml:ns:caldav}calendar-user-type' => 'INDIVIDUAL',
 		];