fix: Don't add empty and broken ExternalShareScanJob on upgrade

This is added manually in
apps/files_sharing/lib/Controller/ExternalSharesController.php when
needed and with arguments.

Signed-off-by: Carl Schwan <carl@carlschwan.eu>

Author: CarlSchwan

apps/files_sharing/appinfo/info.xml

@@ -35,7 +35,6 @@ Turning the feature off removes shared files and folders on the server for all s
 		<job>OCA\Files_Sharing\ExpireSharesJob</job>
 		<job>OCA\Files_Sharing\SharesReminderJob</job>
 		<job>OCA\Files_Sharing\BackgroundJob\FederatedSharesDiscoverJob</job>
-		<job>OCA\Files_Sharing\BackgroundJob\ExternalShareScanJob</job>
 	</background-jobs>
 
 	<repair-steps>

apps/files_sharing/lib/BackgroundJob/ExternalShareScanJob.php

@@ -35,6 +35,10 @@ protected function run($argument): void {
 		}
 
 		[$userId, $path] = $argument;
+		if ($userId === null || $userId === '') {
+			return;
+		}
+
 		try {
 			$this->rootFolder
 				->getUserFolder($userId)