file chooser: Don't react to entry changes in select-folder mode

In select-folder mode, we are putting the directory name into the
entry ourselves. Then the entry appends a /. If we react to this
'spontaneous' change of the entry by clearing the list selection,
this will in turn make us clear the entry. We don't want that.

https://bugzilla.gnome.org/show_bug.cgi?id=726855

gtk/gtkfilechooserwidget.c

@@ -1923,6 +1923,7 @@ static void
 location_entry_changed_cb (GtkEditable          *editable,
                            GtkFileChooserWidget *impl)
 {
+  if (impl->priv->action != GTK_FILE_CHOOSER_ACTION_SELECT_FOLDER)
     reset_location_timeout (impl);
 }