misleading wxASSERT() corrected

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@142 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/common/string.cpp

@@ -289,7 +289,7 @@ void wxString::AllocBeforeWrite(size_t nLen)
     AllocBuffer(nLen);
   }
 
-  wxASSERT( !pData->IsShared() );  // we must be the only owner
+  wxASSERT( !GetStringData()->IsShared() );  // we must be the only owner
 }
 
 // get the pointer to writable buffer of (at least) nLen bytes