handle_message_id() duplicates the contents of the strbuf that is passed
to it. Its only caller proceeds to release the strbuf immediately after
that. Reuse it instead and make that change of object ownership more
obvious by inlining this short function.
Signed-off-by: Rene Scharfe <l.s.r@web.de> Signed-off-by: Junio C Hamano <gitster@pobox.com>