use wxDialog::ShowModal() rather than gtk_dialog_run()
so all the things wxDialog::ShowModal() does are not bypassed


git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_3_0_BRANCH@76227 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775