TreeView: Clear metadata after model update

When the filesystem model is updated, it is rebuilt. This means dangling
indexes inside the TreeView metadata table will have old information and random
directories will toggle open. Clearing the table alleviates this issue.

Libraries/LibGUI/GTreeView.cpp

@@ -250,6 +250,7 @@ void GTreeView::scroll_into_view(const GModelIndex& a_index, Orientation orienta
 
 void GTreeView::did_update_model()
 {
+    m_view_metadata.clear();
     GAbstractView::did_update_model();
     update_content_size();
     update();