avoid forcing a paint on a window with zero size, see #15976

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@75882 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
avoid setting negative window size, see #15976

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@75883 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775