compositor: change rounding in weston_surface_to_buffer_rect()

Rounding both corners of the rectangle down can result in a 0
width/height rectangle before passing to weston_transformed_rect.

This showed up as missing damage in weston-simple-damage (the
bouncing ball would leave green trails when --use-viewport was
used)

Reviewed-by: Daniel Stone <daniels@collabora.co.uk>
Reviewed-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
Signed-off-by: Derek Foreman <derekf@osg.samsung.com>

src/compositor.c

@@ -945,8 +945,8 @@ weston_surface_to_buffer_rect(struct weston_surface *surface,
 	rect.y1 = floorf(yf);
 
 	scaler_surface_to_buffer(surface, rect.x2, rect.y2, &xf, &yf);
-	rect.x2 = floorf(xf);
-	rect.y2 = floorf(yf);
+	rect.x2 = ceilf(xf);
+	rect.y2 = ceilf(yf);
 
 	return weston_transformed_rect(surface->width_from_buffer,
 				       surface->height_from_buffer,