We don't care about size_x variable value and should probably get rid of it
entirely, but for now at least don't update it unnecessarily.
Closes#16834.
git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@78440 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775