Don't emit 'drain' if the stream has been ended. 'drain' should only be emitted if the stream wants more data.

See, https://nodejs.org/api/stream.html#stream_event_drain.

the 'drain' event will be emitted when it is appropriate to resume writing data to the stream.

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• tests and/or benchmarks are included
• documentation is changed or added
• commit message follows commit guidelines

NOTE TO SELF: After this is merged look into emitting 'drain' after state.length < hwm instead of state.length === 0.