lib: objagg: fix handling of object with 0 users when assembling hints

It is possible that there might be an originally parent object with 0
direct users that is in hints no longer considered as parent. Then the
weight of this object is 0 and current code ignores him. That's why the
total amount of hint objects might be lower than for the original
objagg and WARN_ON is hit. Fix this be considering 0 weight valid.

Fixes: 9069a381 ("lib: objagg: implement optimization hints assembly and use hints for object creation")
Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Reviewed-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>