BlockFetch termination failure

[coot]

    termination:                                                FAIL (46.42s)
      *** Failed! Falsified (after 100 tests and 10 shrinks):

...
 
      block-fetch was unstoppable
      Use --quickcheck-replay=223266 to reproduce.
      Use -p '/termination/' to rerun this test only.

Unfortunately, the test case was too long to fit in a GitHub message. We should improve the shrinker.

[coot]

https://ci.iog.io/build/2136000/nixlog/1