LIMIT 0 returns all the results instead of none

InfluxDB ignores the LIMIT clause when it is `LIMIT 0`. This behavior is not documented, and surprising. A client that dynamically computes the LIMIT of a query could end up running a very expensive query because of this.

__Steps to reproduce:__
List the minimal actions needed to reproduce the behavior.

1. Create a measurement `test` with 10 points
2. launch the following query: `SELECT * FROM test LIMIT 0`

__Expected behavior:__
Returns an empty result set

__Actual behavior:__
Returns all the points from the series.

__Environment info:__

* InfluxDB version: InfluxDB vv1.7.6 (git: master 01c8dd416270f424ab0c40f9291e269ac6921964)

Reproduce the issue by creating a measurement with 10 points and running `SELECT * FROM test LIMIT 0`. Trace the query's LIMIT handling and add a regression test; done means the query returns an empty result set instead of all points.

Written by the indexing model from the issue text.