corrected wxTreeCtrl::GetBestSize() for a control with borders

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@43640 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/generic/treectlg.cpp

@@ -3647,4 +3647,14 @@ void wxGenericTreeCtrl::DoDirtyProcessing()
     AdjustMyScrollbars();
 }
 
+wxSize wxGenericTreeCtrl::DoGetBestSize() const
+{
+    wxSize size = wxTreeCtrlBase::DoGetBestSize();
+
+    // The generic control seems to have an implicit border
+    size.IncBy(4, 4);
+
+    return size;
+}
+
 #endif // wxUSE_TREECTRL