clone: check connectivity even if clone is partial

clone: check connectivity even if clone is partial

The commit that introduced the partial clone feature - 548719fbdc
("clone: partial clone", 2017-12-08) - excluded connectivity checks
for partial clones, but this also meant that it is possible for a clone
to succeed, yet not have all objects either present or promised.
Specifically, if cloning with --filter=blob:none from a repository that
has a tag pointing to a blob, and the blob is not sent in the packfile,
the clone will pass, even if the blob is not referenced by any tree in
the packfile.

Turn on connectivity checks for partial clone.

Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>