Fix a little annoyance with combo boxes

Pop up the menu right away, instead of requiring the user to click
again after the button turned into a combobox.

panels/user-accounts/um-editable-combo.c

@@ -278,6 +278,7 @@ static void
 start_editing (UmEditableCombo *combo)
 {
         gtk_notebook_set_current_page (combo->priv->notebook, 2);
+        gtk_combo_box_popup (combo->priv->combo);
 }
 
 static void