tee: -p option should terminate on closed stdout

[jfinkels]

Environment: Ubuntu 20.04, uutils main branch (git commit 20b5365), GNU coreutils v9.5.227-28b1.

Steps to reproduce:

tee -p | :

(The : command means "do nothing").

What happens now: uutils tee waits for stdin indefinitely.

What I expected to happen: GNU tee terminates successfully with no output.

Notes: this appears in the GNU test file tests/misc/tee.sh, though I'm not sure this would resolve the test failure there completely.