Log debug on no response to unbounded read

It's not just not receiving the right number of bytes when there is a
known number of bytes to read that is an issue, but also when there is
no response at all to a read of None bytes (_recv isn't invoked unless
one expects a response).

Author: thormick

pymodbus/transaction.py

@@ -317,6 +317,10 @@ def _recv(self, expected_response_length, full):
             _logger.debug("{} received, "
                           "Expected {} bytes Recieved "
                           "{} bytes !!!!".format(msg_start, total, actual))
+        elif actual == 0:
+            # If actual == 0 and total is not None then the above
+            # should be triggered, so total must be None here
+            _logger.debug("No response received to unbounded read !!!!")
         if self.client.state != ModbusTransactionState.PROCESSING_REPLY:
             _logger.debug("Changing transaction state from "
                           "'WAITING FOR REPLY' to 'PROCESSING REPLY'")