tentative fix for crash in Save As dialog on MacOS with early fltk 1.3

Fltk/menuWindow.cpp

@@ -395,6 +395,9 @@ static void file_save_as_cb(Fl_Widget *w, void *data)
       strcat(pat, NN);
       strcat(pat, formats[i].pat);
     }
+#if defined(HAVE_NATIVE_FILE_CHOOSER) // fix crash in early fltk 1.3.x
+    strcat(pat, NN);
+#endif
   }
 
  test: