Catch specific exceptions (not the parent IMapperException) in StackMapper::findStackFromCardId()

Signed-off-by: Raul Ferreira Fuentes <raul@nextcloud.com>

lib/Db/StackMapper.php

@@ -62,9 +62,10 @@ WHERE c.id = ?
 SQL;
 		try {
 			return $this->findEntity($sql, [$cardId]);
-		} catch (IMapperException $e) {
-			return null;
+		} catch (MultipleObjectsReturnedException|DoesNotExistException $e) {
 		}
+
+		return null;
 	}