Add missing sock.close() to rpc _connect() (#388)

The socket was not closed if the _connect() function timed out.
This lead to an unclosed socket every time a second instance of
pyvisa attempted to connect to a device while the first instance
of pyvisa still had an open connection.

With this fix, the second instance can back off and try again at
a later time without reaching an irrecoverable state.

CHANGES

@@ -5,6 +5,7 @@ PyVISA-py Changelog
 ------------------
 
 - add support for GPIB secondary addresses
+- fix missing sock.close() in rpc _connect()
 
 0.7.0 (05/05/2023)
 ------------------

pyvisa_py/protocols/rpc.py

@@ -437,6 +437,7 @@ def _connect(sock, host, port, timeout=0):
 
         if time.time() >= finish_time:
             # reached timeout
+            sock.close()
             return False
 
         # `select_timout` decreased to 50% of previous or min_select_timeout