Refresh the generic wxDataViewCtrl header if it was made too small.

Refresh the generic wxDataViewCtrl header if it was made too small.

Although normally the control header is not supposed to be resized below its
minimal vertical size, sometimes this can still happen and in this case ugly
artefacts were displayed because it wasn't refreshed properly. Do refresh it
to avoid them.

Closes #13313.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@68212 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775