Check that the connection pointer is not null before trying to call PQfinish after a PostgreSQL connection attempt failure
Check that the connection pointer is not null before trying to call PQfinish after a PostgreSQL connection attempt failure

Also, add some documentation explaining why PQfinish must be called in this instance

Co-Authored-By: Georg Semmler <d0451dd2f55bcd6ffa9a0bbee3d103a0cbd548c8@web.de>
diesel-rs/diesel,sgrif/diesel,sgrif/diesel,diesel-rs/diesel