The error channel in the OVM_ETH migration is buffered. In rare cases, errors were written to this channel in such a way that they were not processed by the collector goroutine. This meant that errors were not being caught by the `lastErr != nil` check, and were instead triggering the total supply check below.

This error reliably reproduces when running the new TestMigrateBalancesRandomMissing test. This test generates a random state, and randomly removes an address/allowance from the witness data. It runs this 100 times per test. We didn't catch this with the other random test because it doesn't exercise the error handling codepath.