Always draw standard-sized checkboxes in generic wxDataViewToggleRenderer.

Always draw standard-sized checkboxes in generic wxDataViewToggleRenderer.

The checkbox should be always shown in its normal size, otherwise it looks
strange. And this also fixes the overflow of the checkbox in the next column
which happened if the size passed to Render() had negative width before.

See #11558.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@62940 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775