add const qualifiers

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

interface/recguard.h

@@ -91,5 +91,5 @@ public:
         (may be simply returning) to prevent reentrant calls to itself.
         If this method returns @false, it is safe to continue.
     */
-    bool IsInside();
+    bool IsInside() const;
 };