allow query end without callback

On a readable stream, if `read` or `on('data')` aren't used then the
stream will not emit the `end` event.
Why? I can't really understand, but maybe you can:
https://github.com/joyent/node/commit/327b6e3e1de88ba1db83142d53b3a57f0d06d519

When a PostgresQuery is created without a callback, `on('data')` isn't
set, so `'end'` never fires, and when using a connection pool, the
connection will not be released.

The solution, as ugly as it may be, is to "kickstart" the readable
stream by calling `.read()`. Consider it a tribute to the Node stream
spectacle.