* drop room pdu linearizer sooner
No point holding onto it while we recheck the db
* move out `missing_prevs` calculation
we're going to need `missing_prevs` whatever we do, so we may as well calculate
it eagerly and just update it if it gets outdated.
* Add another `if missing_prevs` condition
this should be a no-op, since all the code inside the block already checks `if
missing_prevs`
* reorder if conditions
This shouldn't change the logic at all.
* Push down `min_depth` read
No point reading it from the database unless we're going to use it.
* Collect the sent_to_us_directly code together
Move the remaining `sent_to_us_directly` code inside the `if
sent_to_us_directly` block.
* Properly separate the `not sent_to_us_directly` branch
Since the only way this second block is now reachable is if we
*didn't* go into the `sent_to_us_directly` branch, we can replace it with a
simple `else`.
* changelog
