Added wxPropertyGrid::GetUnspecifiedValueText(). Use it instead of assuming that the unspecified value text is always an empty string.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@62955 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/propgrid/propgrid.h

@@ -1239,6 +1239,14 @@ public:
         return m_sortFunction;
     }
 
+    /**
+        Returns (visual) text representation of the unspecified
+        property value.
+
+        @param argFlags For internal use only.
+    */
+    wxString GetUnspecifiedValueText( int argFlags = 0 ) const;
+
     /** Set virtual width for this particular page. Width -1 indicates that the
         virtual width should be disabled. */
     void SetVirtualWidth( int width );