Don't double count data sent on restart

[dirkmc]

Background

When a data transfer is restarted, graphsync emits queue events for all blocks in the file a second time.

This results in OnDataQueued calling revalidator.OnPullDataSent(channel ID, size) with repeat values.

In turn this causes double-counting in the accounting for how many bytes have been sent by the provider. Consequently the provider expects payment for data that has not been sent, and the receiver does not send payment. This causes the retrieval to get stuck.

Solution

We should only call revalidator.OnPullDataSent() the first time a particular block is queued - ie don't call it if the block is re-queued due to a restart.

A bug that may be caused by this issue: filecoin-project/lotus#5901