final w*h interface header reviews

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@55911 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

interface/wx/filefn.h

@@ -101,6 +101,12 @@ public:
 /** @ingroup group_funcmacro_file */
 //@{
 
+/**
+    A special return value of many wxWidgets classes to indicate that
+    an invalid offset was given.
+*/
+const int wxInvalidOffset = -1;
+
 /**
     Under Unix this macro changes the current process umask to the given value,
     unless it is equal to -1 in which case nothing is done, and restores it to