wxUniversal fixes:

window.cpp's WM_CLOSE now calls Close() for wxUniv, else dialogs/
frames won't get closed using system menu/button.
Added missing NULL init for m_artProvider in themes to cure crash
Added 2 sample dsp files for wxUniv (not ideal perhaps but
it will save these getting lost, and much user frustration)


git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@15231 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/univ/themes/metal.cpp

@@ -1183,6 +1183,7 @@ wxMetalTheme::wxMetalTheme()
     m_scheme = NULL;
     m_renderer = NULL;
     m_handlerDefault = NULL;
+    m_artProvider = NULL;
 }
 
 wxMetalTheme::~wxMetalTheme()