fix(carddav): Mark system address book as read-only

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

apps/dav/lib/CardDAV/SystemAddressbook.php

@@ -45,6 +45,7 @@ use Sabre\DAV\Exception\NotFound;
 use Sabre\DAV\ICollection;
 use Sabre\VObject\Component\VCard;
 use Sabre\VObject\Reader;
+use function array_filter;
 use function array_unique;
 
 class SystemAddressbook extends AddressBook {
@@ -296,4 +297,13 @@ class SystemAddressbook extends AddressBook {
 		}
 		throw new Forbidden();
 	}
+
+	public function getACL() {
+		return array_filter(parent::getACL(), function($acl) {
+			if (in_array($acl['privilege'], ['{DAV:}write', '{DAV:}all'], true)) {
+				return false;
+			}
+			return true;
+		});
+	}
 }