Fix crash in wxRegion in wxOSX/Carbon.

Apparently some code expects to be able to call wxRegion::GetWXHRGN() even on
an invalid wxRegion. Return NULL in this case instead of crashing.

This fixes crash on startup of the widgets sample.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@70064 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/osx/carbon/region.cpp

@@ -309,6 +309,9 @@ bool wxRegion::IsEmpty() const
 
 WXHRGN wxRegion::GetWXHRGN() const
 {
+    if ( !m_refData )
+        return NULL;
+
     return M_REGION ;
 }