fix(user_ldap): Ignore unserialize error in group membership migration

The memberships will be checked by the background job later and data
 will be added to the table anyway.

Signed-off-by: Côme Chilliet <come.chilliet@nextcloud.com>

apps/user_ldap/lib/Migration/Version1190Date20230706134108.php

@@ -99,6 +99,10 @@ protected function copyGroupMembershipData(): void {
 		$result = $query->executeQuery();
 		while ($row = $result->fetch()) {
 			$knownUsers = unserialize($row['owncloudusers']);
+			if (!is_array($knownUsers)) {
+				/* Unserialize failed or data was incorrect in database, ignore */
+				continue;
+			}
 			$knownUsers = array_unique($knownUsers);
 			foreach ($knownUsers as $knownUser) {
 				try {