Fix flush_stream hard-error use-after-free

On a hard write error (EPIPE/ECONNRESET) flush_stream did clear_stream()
(sets i_stream_fd = -1) then set_online(false) (adds the user to garbage),
while the user's stream context still had its EV_READ|EV_PERSIST event
armed on the real, still-open fd and held p_context->p_user. If the hourly
gcol::remove_garbage fired before the kernel delivered read EOF, it saw
i_stream_fd < 0 (already cleared) and deleted the user - leaving the
context's p_user dangling (UAF on the later disconnect). (SIGPIPE is
ignored via sign.cpp, so the write returns EPIPE/ECONNRESET safely.)

Fix: remove clear_stream() from the hard-error branch (keep i_stream_fd
>= 0). remove_garbage's skip-open-stream check (zr0) then keeps the user
alive until handle_stream_read (read EOF) reaps the context - the single
reaper - after which remove_garbage deletes it safely. set_online(false)
also removes the user from its room, so room broadcasts stop targeting
the dead fd (no repeated writes). set_online(false)'s b_online guard
makes handle_stream_read's later set_online(false) a no-op (no double
reap).

Verified: abruptly closing a user's stream then posting a room message
reaps the user (online list 1->0) with no crash (0 restarts). Independent
review: APPROVE.

0 files changed, 0 insertions, 0 deletions