[wxGTK2] Don't query native font for underlined, but return the set value - storing...

[wxGTK2] Don't query native font for underlined, but return the set value - storing it natively would likely require
the usage of a PangoAttribute, and I'm not sure if that's even different than just storing it inside wxFontRefData.
Not investigating further as PangoAttribute addition would require ABI compatibility breakage anyhow.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@35272 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775