stream: don't flush destroyed writable
It doesn't make much sense (and is a bit weird) to flush a stream which has been destroyed.
I need help creating a relevant test for this.
Checklist
-
make -j4 test
(UNIX), orvcbuild test
(Windows) passes -
tests and/or benchmarks are included -
documentation is changed or added -
commit message follows commit guidelines
NOTE TO SELF: Look into needFinish & stream destroyed. errorOrDestroy
added in this PR should preferably be async.