Fix gap incorrectly introduced when limited field is missing from sync

Summary:
conduwuit does not return `limited` field from sync if it is not limited. This conforms to the matrix spec because it says this field is optional, and it should be considered limited when "its value is true." libkazv incorrectly assumed this field is present for all sync responses. This caused it to make a gap at the start of the sync batch, and incorrectly try paginate back. If this is an encrypted room, paginating back will cause the previous events to be returned again, erasing the originally decrypted content.

BUG: https://iron.lily-is.land/T134

Test Plan: Build kazv against this. Send a message in an encrypted room. Verify that previous messages does not go undecrypted.

Reviewers: O1 the Kazv Project, servant!

Differential Revision: https://iron.lily-is.land/D163