imap-send: Fix sprintf usage

imap-send: Fix sprintf usage

When composing a command for the imap server, imap-send uses a single
nfsnprintf() invocation for brevity instead of dealing separately with
the case when there is a message to be sent and the case when there
isn’t.  The unused argument in the second case, while valid, is
confusing for static analyzers and human readers.

v1.6.4-rc0~117 (imap-send: add support for IPv6, 2009-05-25)
mistakenly used %hu as the format for an int “port”, by analogy with
existing usage for the unsigned short “addr.sin_port”.  Use %d
instead.

Noticed with clang.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>