Fix read infinite loop in closed socket connection

[ivangonzalezacuna]

During some testings using socketscpi and a Keysight device, I found a bug causing the class to start an infinite loop. The process is:

1. Connect to the SCPI socket of the Keysight device using the connect() function and keep that connection open
2. Then, disconnect the device, so the socket is closed by the server
3. Try to read data using the same socketscpi connection

The while statement is being executed as a loop, because no '\n' is going to be received (the connection is closed). Now it checks if the chunk is empty and raises an Exception in that case, avoiding the infinite loop to happen again when the connection is closed by the server.

Probably the binblockwrite() has a similar problem, but I couldn't check it as I'm not using that function.