Fix segfault on exit from an electron app

[julianmesa-gitkraken]

Now the code close the pollForEvents thread on destroy the NSFW object.
Also added a commit to be able to break (notify) the sleep in the pollForEvents thread, so we will not have to wait the debounceMs time on stopping the watcher or when we are destroying the NSFW object.

[ianhattendorf]

@julianmesa-gitkraken the merge commit for this PR failed CI twice in a row, then passed twice in a row. We should investigate this further and see if there might be some flakiness in the tests.

https://github.com/Axosoft/nsfw/actions/runs/1590191960/attempts/1 (you can view other attempts by changing the URL or going to the latest attempt and then clicking View previous attempt).

[julianmesa-gitkraken]

@julianmesa-gitkraken the merge commit for this PR failed CI twice in a row, then passed twice in a row. We should investigate this further and see if there might be some flakiness in the tests.

https://github.com/Axosoft/nsfw/actions/runs/1590191960/attempts/1 (you can view other attempts by changing the URL or going to the latest attempt and then clicking View previous attempt).

Seems an error conection

Error: Timeout of 120000ms exceeded.

When trying to do a git clone on an external repo: git clone https://github.com/implausible/nsfw-stress-test
Sometimes it occurs locally as well, but rarely.