[hawkff]

AEADChunkWriter.Write takes writeAccess before it writes the length chunk, the payload and the padding. It unlocks only after all three writes succeed. If one of them fails, Write returns with the lock still held, and the next Write on the same writer blocks forever.

This change releases the lock with defer, the same fix that 9b95ab8 applied to StreamChunkWriter.Write.

A regression test makes the first write fail through an upstream writer that always returns an error. It then checks that a second write returns an error instead of blocking. Before this change, the second write blocks and the test fails after two seconds.