No real changes, just fix a harmless warning under OS X.

Don't use "size" variable unnecessarily under non-Mac platforms, this also
fixes a warning about reassigning it immediately after assigning a previous
values to it under Mac.

Closes #16353.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@76789 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775