s3: lib: Fix two old, old bugs in set_conn_connectpath(), now in canonicalize_absolut...

s3: lib: Fix two old, old bugs in set_conn_connectpath(), now in canonicalize_absolute_path().

Canonicalizing a path of /foo/bar/../baz would return /foo/barbaz
as moving forward 3 characters would delete the / character.

Canonicalizing /foo/.. would end up as '\0'.

Test to follow.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=12531

Signed-off-by: Jeremy Allison <jra@samba.org>
Reviewed-by: Uri Simchoni <uri@samba.org>
(backported from commit 82979afc46cc5e466bdd999a94080e7a5df95518)