Don't use protected property rcube_db::$db_error

installer/test.php

@@ -167,7 +167,7 @@ else if ($db_working && $_POST['updatedb']) {
 // test database
 if ($db_working) {
     $db_read = $DB->query("SELECT count(*) FROM {$RCI->config['db_table_users']}");
-    if ($DB->db_error) {
+    if ($DB->is_error()) {
         $RCI->fail('DB Schema', "Database not initialized");
         echo '<p><input type="submit" name="initdb" value="Initialize database" /></p>';
         $db_working = false;

program/include/rcube_contacts.php

@@ -934,8 +934,8 @@ class rcube_contacts extends rcube_addressbook
                 $contact_id
             );
 
-            if ($this->db->db_error)
-                $this->set_error(self::ERROR_SAVING, $this->db->db_error_msg);
+            if ($error = $this->db->is_error())
+                $this->set_error(self::ERROR_SAVING, $error);
             else
                 $added++;
         }