Mistakes can happen with the generation of the progress events, change
knotty to be more tolerant of this rather than crashing, reporting to the
user when something unexpected happens. I haven't debugged why multiple
finish events appear to be triggered.
(Bitbake rev: 7dd06b1016b36420a9c55a45ff29dd64ae1dbcda)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>