Don't reject graphsync unpaid retrievals when unseal price is non-zero

[hannahhoward]

What

When a free retrieval is proposed, it's intercepted by the faster unpaid graphsync retrieval pipeline. This pipeline will fail unless the deal is already unsealed, so no unsealing ever occurs. However, if the SP set an unseal price, the deal will still get rejected here --

boost/retrievalmarket/server/validation.go

Line 130 in 8f84297

if !ask.UnsealPrice.IsZero() || !ask.PricePerByte.IsZero() {

This forces to SP to set UnsealPrice of zero to serve any free retrievals.

I think this check should probably drop the check on UnsealPrice. Under normal conditions in go-fil-markets, GetAsk is a more complicated call that will set Ask parameters based on the sector being unsealed (and will always set the unseal price to zero), so this is equavalent.