catch serial port disconnects in read worker

robot.py

@@ -71,7 +71,11 @@ class Robot:
 
     def serial_read_worker(self):
         while True:
-            self.buffer = self.buffer + self.serial_port.readline()
+            try:
+                self.buffer = self.buffer + self.serial_port.readline()
+            except serial.serialutil.SerialException as e:
+                logger.error(e)
+                break
             if b'\n' in self.buffer:
                 list = self.buffer.split(b'\n', 1)
                 self.buffer = list[1]