display correct start parameter

src/gui_qt/fit/fitwindow.py

@@ -77,16 +77,11 @@ class QFitDialog(QtWidgets.QWidget, Ui_FitDialog):
         w.deleteLater()
         del self.param_widgets[idx]
 
-        if len(self.functionwidget) == 0:
+        self._current_function = None
+        if len(self.param_widgets) == 0:
             # empty model
             self.newmodel_button.setEnabled(False)
             self.deletemodel_button.setEnabled(False)
-            self._current_function = None
-
-        else:
-            f_tree = self.functionwidget.functree
-            func_idx = f_tree.currentItem().data(0, f_tree.counterRole)
-            self._current_function = self.functionwidget.functions[func_idx]
 
     @QtCore.pyqtSlot(int)
     def show_function_parameter(self, function_id: int, function_idx: int = None):