Code review comment for lp://qastaging/~jamesj/openobject-server/complex-cron-fix

I've discovered an issue with this proposal when deploying to another test server. The 'runner' method calls registry['ir.cron']._run_jobs_multithread() to check/run the scheduled tasks, and '_run_jobs_multithread' checks that there are some available threads before processing an ir.cron. I found that '_run_jobs_multithread' was always getting None for the number of threads available.

The solution should be straightforward: the _threads_slots variable should be initialised in 'runner' before going into the loop.