sha1_name.c: avoid unnecessary strbuf_release

sha1_name.c: avoid unnecessary strbuf_release

When we fall back to a standard for_each_reflog_ent() after failing to find
the nth branch switch (or if we had a short reflog) with the call to
for_each_recent_reflog_ent(), we do not need to free the memory allocated
for our strbuf's since a strbuf_reset() will be performed in
grab_nth_branch_switch() before assigning to the entry.

Plus, the strbuf_release() negates the non-zero hint we initially gave to
strbuf_init() just above these lines.

Signed-off-by: Brandon Casey <drafnel@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>