curl-glue: catch libcurl attempting to change timeout handler when we destroy a curl...

curl-glue: catch libcurl attempting to change timeout handler when we destroy a curl context on exit

If we destroy both an event loop and a curl contect object at the same
time, then we get into this weird situation where curl wants us to
reconfigure a timout event source right before destruction, which
sd-event will refuse however, since it is already being shutdown.

Hence, catch that and simply don't bother adjusting the timeout, since
we cannot get back from there anyway.