store OOB status along with members, to avoid unneccesary fetching
for some small rooms, it is possible that calling /members would not
yield any previously unknown members, as they were all recently active.
This would be the case for most DMs.
For these rooms, we'd end up with 0 OOB members after lazy loading them,
so when getting them out of storage we need a way to distuinguist this case
from never having lazy loaded the members of the room at all.
We store a marker object in the same store and return [] or null accordingly.
This way the /members don't get fetched a second time.
matrix-js-sdk
5e11bf73 - store OOB status along with members, to avoid unneccesary fetching
