git-send-email: fix missing space in error message

git-send-email: fix missing space in error message

When the command cannot make a connection to the SMTP server the error
message to diagnose the broken configuration is issued.  However, when an
optional smtp-server-port is given and needs to be reported, the message
lacked a space between "hello=<smtp-domain>" and "port=<smtp-server-port>".

Signed-off-by: Sylvain Rabot <sylvain@abstraction.fr>
Signed-off-by: Junio C Hamano <gitster@pobox.com>