fix: Prevent crash when refreshing metadata for files without an owner

This crash was mostly happening when using external storages and for example the command "occ memories:migrate-google-takeout"

Signed-off-by: Vincent FarZz <farcry69@live.fr>

lib/private/FilesMetadata/FilesMetadataManager.php

@@ -122,7 +122,7 @@ public function refreshMetadata(
 				return $this->refreshMetadata($node, self::PROCESS_BACKGROUND);
 			}
 
-			$this->jobList->add(UpdateSingleMetadata::class, [$node->getOwner()->getUID(), $node->getId()]);
+			$this->jobList->add(UpdateSingleMetadata::class, [$node->getOwner()?->getUID(), $node->getId()]);
 		}
 
 		return $metadata;