receiver: use None for serial number of c534

lib/logitech_receiver/receiver.py

@@ -342,7 +342,7 @@ class Receiver(object):
 			self.serial = _strhex(serial_reply[1:5])
 			self.max_devices = ord(serial_reply[6:7])
 		else:
-			self.serial = 0
+			self.serial = None
 			self.max_devices = 6
 
 		if self.product_id == 'c539' or self.product_id == 'c53a' or self.product_id == 'c53f':

lib/solaar/cli/__init__.py

@@ -98,7 +98,7 @@ def _find_receiver(receivers, name):
 	assert name
 
 	for r in receivers:
-		if name in r.name.lower() or name == r.serial.lower():
+		if name in r.name.lower() or (r.serial is not None and name == r.serial.lower()):
 			return r