API docs: LSIF: correct race condition in documentation data queues

Created by: slimsag

There was a race condition here: If the src channel of the queue was closed and had no more data, but the buffer had not yet been flushed, then the dst channel would be closed - dropping all buf values that were still waiting to be written to the dst channel.

This seems to have been one of the issues leading to inconsistent usage examples on API docs pages (you'd get no results in such instances.)

This file is clearly the most complex part of the API docs backend implementation, and as such I am rethinking how it is structured and how to test it. I'll send more PRs for this later.

Signed-off-by: Stephen Gutekanst [email protected]