add const qualifiers

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

interface/wfstream.h

@@ -90,7 +90,7 @@ public:
     /**
         Returns @true if the stream is initialized and ready.
     */
-    bool IsOk();
+    bool IsOk() const;
 };
 
 
@@ -133,7 +133,7 @@ public:
     /**
         Returns @true if the stream is initialized and ready.
     */
-    bool IsOk();
+    bool IsOk() const;
 };
 
 
@@ -176,7 +176,7 @@ public:
     /**
         Returns @true if the stream is initialized and ready.
     */
-    bool IsOk();
+    bool IsOk() const;
 };
 
 
@@ -221,7 +221,7 @@ public:
     /**
         Returns @true if the stream is initialized and ready.
     */
-    bool IsOk();
+    bool IsOk() const;
 };