fixes a bug, where an exception occurs when current is not read correctly

modules/chambercontroller.py

@@ -382,8 +382,8 @@ class ChamberController(Module):
             #time.sleep(0.1)
             #self.actual_current = 
             current = protocol.get_actual_current()
-            # TODO(rh): Test this!
-            self.mqtt_client.publish(self.mqtt_topic_prefix+"current", pack("d", current), qos=2)
+            if current is not None:
+                self.mqtt_client.publish(self.mqtt_topic_prefix+"current", pack("d", current), qos=2)
             # self.publish()
             # logger.log("delta={:05.2f} delta_ambient={:05.2f} delta_current={:05.2f} voltage={:05.2f} v_out={:05.2f} v_actual={:05.2f} i_actual={:05.2f} pid_sum={:05.2f}".format(delta, delta_ambient, delta_current, self.voltage, v_out, self.actual_voltage, self.actual_current, self.pid.sum))
         except AssertionError as e: