Log.difference behaviour

[latenssi]

Referring to this line of code: log.js#L581

When this is using a._headsIndex I get an empty log back when comparing 2 logs with same head but the other one having a longer history (more entries loaded from local filesystem). If I monkeypatch (as seen here) this to use a._entryIndex I get back what I would l logically expect (log with entries which are in the other but not in the other).

@thiagodelgado111 Would you consider the change I made a sound one and should we implement it in ipfs-log or am I missing something?