BUG/MEDIUM: checks: Subscribe to I/O events only if a mux was installed

In the commit 2fabd9d53 ("BUG/MEDIUM: checks: Subscribe to I/O events on an
unfinished connect"), we force the subscribtion to I/O events when a new
connection is opened if it is not fully established. But it must only be done if
a mux was immediately installed. If there is no mux, no subscription must be
performed.

No backport needed.
1 file changed