compose recipients validation logic

[tomholub]

I'm not too sure about this - the validation happens asynchronously as a task. Would that be of any use? By the time it figures out it's wrong, this method may already finish.

Originally posted by @tomholub in #821 (comment)

[sosnovsky]

It's just for UI, because when recipient is selected then user won't be able to see if it's highlighted with red or orange color. Evaluation result isn't used for determining valid recipients.

[tomholub]

What would happen if these two lines were removed from ComposeViewController.sendMessage?

[sosnovsky]

Here are example videos - to reproduce you just need to add some invalid recipient (expired or revoked), then tap on it to select and try to send email.

Here how it works with these 2 lines (recipient highlighted after showing error modal):
https://user-images.githubusercontent.com/1062093/139436192-78a41417-7f83-4e5a-9437-318522e9dbe0.mp4

And without (recipient stays gray, because of selected state)
https://user-images.githubusercontent.com/1062093/139436265-4c61107a-e55d-4e99-b814-925167b6ea00.mp4