LibGUI: Model-less views should not swallow key events

At least pass them up to GUI::Widget so they can be handled there.

Libraries/LibGUI/ListView.cpp

@@ -196,7 +196,7 @@ void ListView::mousemove_event(MouseEvent& event)
 void ListView::keydown_event(KeyEvent& event)
 {
     if (!model())
-        return;
+        return AbstractView::keydown_event(event);
 
     if (event.key() == KeyCode::Key_Escape) {
         if (on_escape_pressed)

Libraries/LibGUI/TableView.cpp

@@ -170,7 +170,7 @@ void TableView::paint_event(PaintEvent& event)
 void TableView::keydown_event(KeyEvent& event)
 {
     if (!model())
-        return;
+        return AbstractTableView::keydown_event(event);
 
     AbstractTableView::keydown_event(event);
 

Libraries/LibGUI/TreeView.cpp

@@ -433,7 +433,7 @@ void TreeView::did_update_selection()
 void TreeView::keydown_event(KeyEvent& event)
 {
     if (!model())
-        return;
+        return AbstractTableView::keydown_event(event);
 
     if (event.key() == KeyCode::Key_Space) {
         if (model()->row_count(cursor_index()))