Fix issue #10581

Fix issue #10581.

I'm not getting any more timeouts with the 0.17.5-2 minion with this change running:
2x ```while :; do salt winminion test.sleep 10```. Previously this would always timeout as find_job will be called.
1x ```while :; do salt winminion test.ping```. Just to throw lots of very short lived jobs at the minion at the same time to try to trigger any really obvious threading issues.

Running the tests on linux with multiprocessing=False also looks good.