ENSIndexer: `null` topics in `event.log.topics`?

[shrugs]

• figure out why we're getting null topics in our decoding, which should only happen with an event log / abi mismatch (i.e. the event can be mostly decoded)
• maaaaybe not an issue at all? but probably an issue

[shrugs]

figured it out, ponder internal decoding issue, mitigated and documented in #1744