Fix size of the icon returned from wxFSVolume::GetIcon().

Calling SetHICON() is not enough, the icon size already needs to be set or,
even better, CreateFromHICON(), which does both atomically, should be used.

Closes #16672.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@78116 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775