There is no need to build a copy of the relevant part of the string just
to make sure we have a NUL-terminated string. We can simply pass the
length of the interesting part to dwim_ref() instead.
Signed-off-by: Rene Scharfe <rene.scharfe@lsrfire.ath.cx> Signed-off-by: Junio C Hamano <gitster@pobox.com>