rescan: allow filter re-query for duplicate block notifications
rescan: allow filter re-query for duplicate block notifications

In this commit, we fix an existing bug that would prevent us from
properly re-trying to fetch a block in the case that our set of
connected peers didn't have the block, or was unable to reply to us.
Before this commit, the second time we went to fetch the block, we would
skip it as we didn't have the filter for the _next_ block. This is fine
if it's the case that we hadn't already processed the block, but in this
case for retries we update our current stamp.

lightninglabs/neutrino