bpo-31647: Fix write_eof() after close() for SelectorSocketTransport (GH-7149) (GH-7153)

Fixed bug where calling write_eof() on a _SelectorSocketTransport after
it's already closed raises AttributeError.
(cherry picked from commit 23f587e395e41bd5e116312b036183f42bc4159b)

Co-authored-by: twisteroid ambassador <twisteroidambassador@users.noreply.github.com>
3 files changed