[mutter] idle-monitor: Reset timeout before firing watch

[Georges Basile Stavracas Neto <gbsneto src gnome org>]

commit 0e69fe07819a289f3156f18c46b749b2f128cf05
Author: Jonas Ådahl <jadahl gmail com>
Date:   Mon Sep 16 16:36:51 2019 +0200

    idle-monitor: Reset timeout before firing watch
    
    The watch might be removed during firing, meaning the source is
    destroyed after returning. Avoid use-after-free by unsetting the timeout
    before firing. Returning G_SOURCE_CONTINUE in that case is harmless, as
    source is destroyed.
    
    Fixes: https://gitlab.gnome.org/GNOME/mutter/issues/796
    
    https://gitlab.gnome.org/GNOME/mutter/merge_requests/799

 src/backends/meta-idle-monitor.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)
---
diff --git a/src/backends/meta-idle-monitor.c b/src/backends/meta-idle-monitor.c
index e5124abc1..9fa481742 100644
--- a/src/backends/meta-idle-monitor.c
+++ b/src/backends/meta-idle-monitor.c
@@ -324,9 +324,10 @@ idle_monitor_dispatch_timeout (GSource     *source,
   if (ready_time > now)
     return G_SOURCE_CONTINUE;
 
-  meta_idle_monitor_watch_fire (watch);
   g_source_set_ready_time (watch->timeout_source, -1);
 
+  meta_idle_monitor_watch_fire (watch);
+
   return G_SOURCE_CONTINUE;
 }