use time for interpolation pf empty dsc reference to avoid infs

src/gui_qt/dsc/glass_dialog.py

@@ -86,6 +86,8 @@ class TgCalculator(QtWidgets.QWizard, Ui_DSCEvalDialog):
         self.next_button.clicked.connect(lambda: self.stackedWidget.setCurrentIndex((self.stackedWidget.currentIndex() + 1) % 3))
         self.back_button.clicked.connect(lambda: self.stackedWidget.setCurrentIndex((self.stackedWidget.currentIndex() + 2) % 3))
 
+        self.listWidget.itemChanged.connect(self.change_visibility)
+
     def __call__(self):
         self.clear()
         self._colors = cycle(Tab10)