http-push: add trailing slash at arg-parse time, instead of later on

http-push: add trailing slash at arg-parse time, instead of later on

That way, we don't have to update repo->path and repo->path_len again
after adding the trailing slash.

Signed-off-by: Tay Ray Chuan <rctay89@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>