Fix setpoint line label to not display old values

Setpoint line still displays 0 °C sometimes!

pytec/tec_qt.py

@@ -216,10 +216,10 @@ class ChannelGraphs:
             self._t_line.setVisible(visible)
         if temp is not None:
             self._t_line.setValue(temp)
-            if visible is False:
-                # PyQtGraph does not update this text when the line
-                # is not visible, but we need it so that the temperature
-                # label doesn't display 0 °C despite not being at 0 °C.
+
+            # PyQtGraph normally does not update this text when the line
+            # is not visible, so make sure that the temperature label 
+            # gets updated always, and doesn't stay at an old value.
             self._t_line.label.setText(f"{temp} °C")