On the other backends we will get some sort of expose event after
showing the stage's window which will queue a redraw. These expose
events don't exist on Wayland so nothing will cause Clutter to queue a
redraw. Weston doesn't bother displaying anything for the stage's
surface until the first buffer is sent, which of course it will never
receive if Clutter doesn't paint anything. This patch just makes it
explicitly queue a redraw after the stage is shown so that we will
always pass at least one frame to the compositor.

The bug can be seen by running test-stage-sizing. That example doesn't
have any animations so it won't try to queue any redraws until
something interacts with it. On the other hand something like
test-actors works fine without the patch because it constantly queues
redraws anyway in order to display the animation.