shell: Schedule repaint when moving a surface

It seems we used to rely on the repaint scheduled by the cursor motion.
But if there's no cursor, there's no cursor motion, so we need to schedule
our own repaint.
diff --git a/src/shell.c b/src/shell.c
index f7369f3..6333180 100644
--- a/src/shell.c
+++ b/src/shell.c
@@ -782,6 +782,8 @@
 
 	weston_surface_configure(es, dx, dy,
 				 es->geometry.width, es->geometry.height);
+
+	weston_compositor_schedule_repaint(es->compositor);
 }
 
 static void