When there is no wallet, filter out priced deals from query responses

[rvagg]

Currently they are just sorted lower, but if we can't pay then we shouldn't even attempt:

autoretrieve/filecoin/retriever.go

Line 200 in 1d2d50a

if a.UnsealPrice.IsZero() && !b.UnsealPrice.IsZero() {

Filclient will fail on these after trying to set up a payment channel and failing.