add const qualifiers

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@52414 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

interface/iconloc.h

@@ -35,5 +35,5 @@ public:
         Returns @true if the object is valid, i.e. was properly initialized, and
         @false otherwise.
     */
-    bool IsOk();
+    bool IsOk() const;
 };