Don't append extension if it contains wildcards in wxGTK wxFileDialog.

Restore the test for wildcards erroneously removed in r74307.

Closes #15285.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@74322 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775