Based on patches by Johannes Baiter <johannes.baiter@bsb-muenchen.de>
and Calin Don.

If of.err is 0, it means that there was a memory allocation error
and no further logging and/or processing is needed.  The of.failed
string can be only accessed if of.err is not 0.

The ev->timedout flag is set on first timer expiration, and never reset
after it.  Due to this the code to stop the timer when the timer was
canceled never worked (except in a very specific time frame immediately
after start), and the timer was always armed again.  This essentially
resulted in a buffer flush at the end of an event loop iteration.

This behaviour actually seems to be better than just stopping the flush
timer for the whole shutdown, so it is preserved as is instead of fixing
the code to actually remove the timer.  It will be further improved by
upcoming changes to preserve cancelable timers if there are other timers
blocking shutdown.