add IsOk() to all classes having Ok() method (patch 1570985)

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@41751 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/os2/pngread.h

@@ -88,7 +88,8 @@ public:
   virtual bool InstantiateBitmap(wxBitmap *bitmap);
   wxMask *CreateMask(void);
 
-  inline bool Ok(void) { return imageOK; }
+  inline bool Ok() const { return IsOk(); }
+  inline bool IsOk(void) { return imageOK; }
 };
 
 class wxPNGReaderIter