safer destruction of wxXmlResource::ms_instance

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@13641 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

contrib/src/xrc/xmlres.cpp

@@ -1112,7 +1112,7 @@ public:
     }
     void OnExit()
     {
-        delete wxXmlResource::Get();
+        delete wxXmlResource::Set(NULL);
         CleanXMLID_Records();
     }
 };

src/xrc/xmlres.cpp

@@ -1112,7 +1112,7 @@ public:
     }
     void OnExit()
     {
-        delete wxXmlResource::Get();
+        delete wxXmlResource::Set(NULL);
         CleanXMLID_Records();
     }
 };