Fix Main Task Synchronization

[thestr4ng3r]

This fixes some delicate race conditions.

From now on, when accessing the RCore in CutterCore, we must always use CORE_LOCK(); and access it like core->... and everything will be fine.

[ITAYC0HEN]

Approved.
With that, you just stated a very important thing:

From now on, when accessing the RCore in CutterCore, we must always use CORE_LOCK(); and access it like core->... and everything will be fine.

This, in more details, should go to the dev documentation and be told to the dev team

[thestr4ng3r]

It's documented for the core_ member, so one can see it when looking for how to access the RCore. But yeah can be made more clear in general.