fix events API timeout handling for nil blocks

[dirkmc]

The events API timeout handler does not take into account nil blocks.
This PR fixes it, and adds a test for deal expiry.

[raulk]

This is an awesome find! Great that we also extended the test coverage significantly for this edge case 👏

Just need to fix the lint and the test failures, which complain about deal expiration bounds. Not sure if this is related to us modifying the miner actor configuration. It shouldn't be because each test runs in a separate process in CI, so there shouldn't be any cross interaction. Regardless, we should probably reset the value of minerN.DealMinDuration to the original values with a t.Cleanup().

Maybe related to the introduction of MinBlocksDuration? Although not sure how, because everywhere continues using the zero value.

[raulk]

I just noticed that this will end up conflicting with #7000, which does an entire rewrite of these components.

@dirkmc -- just to have an extra data point, could you try running the test in here against #7000?

[dirkmc]

Oh hmm good point 👍

I tried running the test against #7000 and it failed, so I guess we will need the fix here in addition to those changes.

[Stebalien]

Oh, wow. I didn't even notice this issue.

[Stebalien]

Any reason not to merge this directly to master?