xdg-shell: fix maximizing in multi-head setup

Set the right position of maximized window. Up until now we ignored
output's "position" and were using only the working area
of output which is in output-relative coordinates. This led to
showing the maximized window always on the first output.

This, along with the previous patch, fixes
https://bugs.freedesktop.org/show_bug.cgi?id=82967

Signed-off-by: Marek Chalupa <mchqwerty@gmail.com>
Reviewed-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>

desktop-shell/shell.c

@@ -5291,15 +5291,16 @@ set_maximized_position(struct desktop_shell *shell,
 {
 	int32_t surf_x, surf_y;
 	pixman_rectangle32_t area;
+	pixman_box32_t *e;
 
-	/* use surface configure to set the geometry */
 	get_output_work_area(shell, shsurf->output, &area);
 	surface_subsurfaces_boundingbox(shsurf->surface,
 					&surf_x, &surf_y, NULL, NULL);
+	e = pixman_region32_extents(&shsurf->output->region);
 
 	weston_view_set_position(shsurf->view,
-				 area.x - surf_x,
-				 area.y - surf_y);
+				 e->x1 + area.x - surf_x,
+				 e->y1 + area.y - surf_y);
 }
 
 static void