[mutter] screen: Unset timeout ID after removal

[Florian Müllner <fmuellner src gnome org>]

commit 34207ba5097768f5f72fb84cb175bc2f60ceab95
Author: Florian Müllner <fmuellner gnome org>
Date:   Thu Sep 28 15:09:31 2017 +0200

    screen: Unset timeout ID after removal
    
    Otherwise we may try to remove the now invalid ID again, resulting
    in a warning.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=788292

 src/core/screen.c |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)
---
diff --git a/src/core/screen.c b/src/core/screen.c
index 99ab5d7..82ad386 100644
--- a/src/core/screen.c
+++ b/src/core/screen.c
@@ -1480,6 +1480,7 @@ meta_screen_hide_tile_preview (MetaScreen *screen)
 {
   if (screen->tile_preview_timeout_id > 0)
     g_source_remove (screen->tile_preview_timeout_id);
+  screen->tile_preview_timeout_id = 0;
 
   meta_compositor_hide_tile_preview (screen->display->compositor);
 }