Don't always automatically switch to an epoch when finding it

Making this logic more refined https://github.com/ssbc/ssb-tribes2/pull/78#discussion_r1159461684

Idk if this is a concrete todo yet or if this will maybe resolve itself when we fix other issues, as well as @mixmix working on the "preferred epoch" logic

situations we've found so far:

[ ] https://github.com/ssbc/ssb-tribes2/blob/d3073f2217860a27852806ac5a43bc11e9077a40/index.js#L462
[ ] https://github.com/ssbc/ssb-tribes2/blob/460573888f9ece108beec3772ee6c2ed05f68cf8/index.js#L444-L445

ssbc / ssb-tribes2

Don't always automatically switch to an epoch when finding it #87