init-db: silence template_dir leak when converting to absolute path

template_dir starts off pointing to either argv or nothing. However if
the value supplied in argv is a relative path, absolute_pathdup() is
used to turn it into an absolute path. absolute_pathdup() allocates
a new string, and we then "leak" it when cmd_init_db() completes.

We don't bother to actually free the return value (instead we UNLEAK
it), because there's no significant advantage to doing so here.
Correctly freeing it would require more significant changes to code flow
which would be more noisy than beneficial.

Signed-off-by: Andrzej Hunt <ajrhunt@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>