fix invisible multi-line wxTextCtrl selection when custom foreground/background color is used with GTK3
closes #16176


git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_3_0_BRANCH@76308 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775