Do not list system users in contacts menu if sharing autocompletion is disabled

Signed-off-by: Christoph Wurst <christoph@winzerhof-wurst.at>

apps/dav/appinfo/app.php

@@ -50,7 +50,13 @@ $eventDispatcher->addListener('OCP\Federation\TrustedServerEvent::remove',
 $cm = \OC::$server->getContactsManager();
 $cm->register(function() use ($cm, $app) {
 	$user = \OC::$server->getUserSession()->getUser();
-	if (!is_null($user)) {
-		$app->setupContactsProvider($cm, $user->getUID());
+	if (is_null($user)) {
+		return;
 	}
+	if (\OC::$server->getConfig()->getAppValue('core', 'shareapi_allow_share_dialog_user_enumeration', 'yes') !== 'yes') {
+		// Don't include system users
+		// This prevents user enumeration in the contacts menu and the mail app
+		return;
+	}
+	$app->setupContactsProvider($cm, $user->getUID());
 });