t6050 (replace): fix bogus "fetch branch with replacement" test

t6050 (replace): fix bogus "fetch branch with replacement" test

The test was missing some "&&" at the end of some lines and it
was wrong because, as the replacement refs were not fetched,
the commits from the parallel branch should not show up. This
was found by Elijah Newren.

This is fixed by checking that after the branch from HASH6 is
fetched, the commits from the parallel branch don't show up,
and then by fetching the replacement refs and checking that
they do show up afterwards.

Signed-off-by: Christian Couder <chriscool@tuxfamily.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>