unlock event queue when handling event.

[xpol]

1. unlock event queue when handling event.
2. and make lock scope smaller.

[cynron]

@xpol

I'm afraid PC_PRE_ALLOC_SET_IDLE inside pc__handle_event should be protected by event_mutex as we release the mutex before entering pc__handle_event

Thanks!

[xpol]

@cynron
Sorry.
This is last day that I work on lua-pomelo (going for another job), and I can get it working.
I'm considering shutdown lua-pomelo.

Thanks for you great help and good luck to you!