fix: Ensure CLOUD key exists before resolving Cloud ID

Signed-off-by: Enjeck C <patrathewhiz@gmail.com>

Author: enjeck

lib/private/Collaboration/Collaborators/MailPlugin.php

@@ -160,6 +160,9 @@ public function search($search, $limit, $offset, ISearchResult $searchResult): b
 
 						if ($this->shareeEnumeration) {
 							try {
+								if (!isset($contact['CLOUD'])) {
+									continue;
+								}
 								$cloud = $this->cloudIdManager->resolveCloudId($contact['CLOUD'][0] ?? '');
 							} catch (\InvalidArgumentException $e) {
 								continue;