compositor: ignore views on other outputs during compositor_accumulate_damage()

compositor_accumulate_damage() is called for each output during repaint. The DRM backend will only set keep_buffer for the surfaces that are visible on the current output. So a buffer_ref is released that may still be needed. When the output that shows the surface is repainted, the buffer_ref is gone and the surface cannot be put on a plane.

Ignore all surfaces that are not visible on the current output to avoid this.

Signed-off-by: Michael Olbrich m.olbrich@pengutronix.de