Deselect all items in wxMSW wxListBox when selection is set to -1.

Deselect all items in wxMSW wxListBox when selection is set to -1.

Even though this behaviour is somewhat counterintuitive, the documentation
mentions that this is what should happen and wxGTK and wxOSX already behave
like this so bring wxMSW in line.

wxListBox::DeselectAll() should probably just call SetSelection(wxNOT_FOUND)
when the item to leave selected is not specified too now.

Closes #12705.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@66243 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775