[gnome-control-center] printers: Fix autoptr object not being initialized to NULL.

[Marek Kašík <mkasik src gnome org>]

commit 7bbbef5fdee994e08c39e3b9e6b5ba831b22229f
Author: Robert Ancell <robert ancell canonical com>
Date:   Mon Nov 2 09:25:04 2020 +1300

    printers: Fix autoptr object not being initialized to NULL.
    
    Won't cause a problem in this case but should be done for safety.
    
    Introduced in ad226b420c656a055602136ff1feaa6ba919d039

 panels/printers/pp-utils.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/panels/printers/pp-utils.c b/panels/printers/pp-utils.c
index ca849bc2b..8dc86f057 100644
--- a/panels/printers/pp-utils.c
+++ b/panels/printers/pp-utils.c
@@ -2710,7 +2710,7 @@ get_all_ppds_async (GCancellable *cancellable,
                     gpointer      user_data)
 {
   GAPData          *data;
-  g_autoptr(GThread) thread;
+  g_autoptr(GThread) thread = NULL;
   g_autoptr(GError)  error = NULL;
 
   data = g_new0 (GAPData, 1);