Always initialize SelectInHDC::m_hgdiobj in wxMSW.

Always initialize SelectInHDC::m_hgdiobj in wxMSW.

Leaving m_hgdiobj uninitialized probably didn't result in any problems
considering how this class is currently used but it did result in g++ warnings
about uninitialized member with aggressive warning flags and also could easily
become a problem in the future so just ensure that we always initialize it.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@68099 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775