compositor: fix input events propagated through locked screen

The lock() function on shell.c is hiding all layers before locking the screen, and after that it puts the compositor in sleeping state. With the compositor in sleeping state, the display is not repainted, and that causes the hiding of the layers to be delayed until the first event, which fires a repaint request. The problem is that this event is already dispatched to the application before the Unlock dialog comes up.

Fixes: #569 (closed)

Signed-off-by: ekapllaj elv.kapllaj@gmail.com