Blender Git Loki

Fix memory leak in GHOST Event Manager.

The events are allocated on the heap, then pushed on a stack. Before
being processed, they are popped from the stack, and deleted after
processing is done. When the manager is destroyed (e.g. application
closing), any remaining event in the stack is detroyed.

Issue is that when the "application closing" event is processed, it is
never freed, because the manager gets destroyed before the call to
`delete` is made and the event is not on the stack anymore.

Now events are left on the stack while they are processed, and only
popped and deleted after processing is done.

As a slight bonus refactor: use void as return type for dispatch events
functions, as no caller is checking the return value, and it is not
clear what it means (suggested by the reviewer).

Reviewers: brecht

Differential Revision: https://developer.blender.org/D1695