Correctly handle the case when write happens after close

[normanmaurer]

Motivation:

When writing to a closed or shutdown QuicStreamChannel we should fail the write directly with the right exception without validating the type first. This is what we do in other Channels as well so we should be consistent

Modifications:

• Check first if the Channel is still ready for writes and if not fail the write directly and all queued writes
• Add unit tests

Result:

More consistent behaviour