clutter/main: Update event actor after event was sitting in the queue
Apparently the source actor events can change while an event is sitting inside the stage queue, for example when a window gets closed in response to a wayland client handling an event.
Now when we're done queuing and compressing events and finally emit them to Clutter, events can have an outdated source actor pointer, leading to a crash.
To fix this, ask the stage for the current device actor again and update the event source actor before emitting the event to Clutter.
Fixes: #2152 (closed)