* Fetch all conversations on startup of app, not on inbox load
A recent change to fetch conversations less didn't take into account all
that can happen in the app without the inbox loaded. That only happens
when the window is shown, and messages can come in with the app in the
background. In that case, the conversation wouldn't have been loaded
from the database, but would be saved to the database anyway, losing
data.
This change fetches all conversations as soon as the the data store is
ready for a fetch. It also introduces failsafe throws to ensure that
synchronous ConversationController accesses don't happen until the
initial fetch is complete. A new getUnsafe() method was required to
account for some of the model setup that happens during that initial
conversation fetch.
Fixes#1428
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* Fix tests: ConversationController.load() required before get()
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