pretty: simplify output line length calculation in pp_user_info()

pretty: simplify output line length calculation in pp_user_info()

Keep namelen unchanged and don't use it to hold a value that we're not
interested in anyway -- we can use maillen and the constant part
directly instead.  This simplifies the code slightly and prepares for
the next patch that makes use of the original value of namelen.

Signed-off-by: Rene Scharfe <rene.scharfe@lsrfire.ath.cx>
Signed-off-by: Junio C Hamano <gitster@pobox.com>