`engine.Query` queues up a bunch of `defer` functions that (among other
things) wait for various resources to clean themselves up.
In `query`, we have a "naive" (read: bad) `eventEmitter`, whose `done`
channel is set to `nil`. Therefore, the relevent `defer` waits for an
event on a `nil` channel which in Go will famously simply hang forever.
This commit will correct this by setting this channel appropriately, so
that it signals appropriately when it's done.
628abb5636