fixup! Fix sync errors for duplicate cards with the same UID for different backends

Author: miaulalala

apps/dav/lib/CardDAV/Converter.php

@@ -47,13 +47,13 @@ public function createCardFromUser(IUser $user): ?VCard {
 		$userProperties = $this->accountManager->getAccount($user)->getProperties();
 
 		$uid = $user->getUID();
-		$name = $user->getBackendClassName();
+		$backendClassName = $user->getBackendClassName();
 		$cloudId = $user->getCloudId();
 		$image = $this->getAvatarImage($user);
 
 		$vCard = new VCard();
 		$vCard->VERSION = '3.0';
-		$vCard->UID = "$name:$uid";
+		$vCard->UID = "$backendClassName:$uid";
 	 	$vCard->add(new Text($vCard, 'X-NEXTCLOUD-UID', $uid));
 
 		$publish = false;

apps/dav/lib/CardDAV/SyncService.php

@@ -329,7 +329,7 @@ public function syncInstance(\Closure $progressCallback = null) {
 		$allCards = $this->backend->getCards($systemAddressBook['id']);
 		foreach ($allCards as $card) {
 			$vCard = Reader::read($card['carddata']);
-			$uid = $vCard->{'X-NEXTCLOUD-UID'}->getValue();
+			$uid = $vCard->{'X-NEXTCLOUD-UID'}->getValue() ?? $vCard->{'UID'}->getValue();
 			// load backend and see if user exists
 			if (!$this->userManager->userExists($uid)) {
 				$this->deleteUser($card['uri']);