[glib] gpollfilemonitor: Fix use-after-free caused by leaking GSource

[Philip Withnall <pwithnall src gnome org>]

commit ba4a9538e14e8ba0ea037cab5f4b23aa47272a4c
Author: Ting-Wei Lan <lantw src gnome org>
Date:   Tue Mar 20 21:58:20 2018 +0800

    gpollfilemonitor: Fix use-after-free caused by leaking GSource
    
    https://bugzilla.gnome.org/show_bug.cgi?id=794528

 gio/gpollfilemonitor.c | 2 ++
 1 file changed, 2 insertions(+)
---
diff --git a/gio/gpollfilemonitor.c b/gio/gpollfilemonitor.c
index 411e00393..bd3d78a02 100644
--- a/gio/gpollfilemonitor.c
+++ b/gio/gpollfilemonitor.c
@@ -50,7 +50,9 @@ g_poll_file_monitor_finalize (GObject* object)
   
   poll_monitor = G_POLL_FILE_MONITOR (object);
 
+  g_poll_file_monitor_cancel (G_FILE_MONITOR (poll_monitor));
   g_object_unref (poll_monitor->file);
+  g_clear_object (&poll_monitor->last_info);
 
   G_OBJECT_CLASS (g_poll_file_monitor_parent_class)->finalize (object);
 }