Fix wxFont construction from default wxFontInfo in wxMSW.

Don't use -1 as the real point size.

Also update the font sample to allow testing such font.

Closes #16468.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_3_0_BRANCH@77494 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775