[gnome-online-accounts] providerfactory: Add 'error' precondition

[Debarshi Ray <debarshir src gnome org>]

commit ce41bf4b42dbe686d90a3f78cbf389f8a0fd2e5f
Author: Christophe Fergeau <cfergeau redhat com>
Date:   Sat Mar 26 12:43:31 2016 +0100

    providerfactory: Add 'error' precondition
    
    Ensure that the 'error' parameter is either NULL, or pointing to a NULL
    value.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=764157

 src/goabackend/goaproviderfactory.c |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)
---
diff --git a/src/goabackend/goaproviderfactory.c b/src/goabackend/goaproviderfactory.c
index a0df2a2..87a1734 100644
--- a/src/goabackend/goaproviderfactory.c
+++ b/src/goabackend/goaproviderfactory.c
@@ -129,6 +129,7 @@ get_providers_finish_default (GoaProviderFactory  *factory,
   gboolean had_error;
 
   g_return_val_if_fail (g_task_is_valid (result, factory), FALSE);
+  g_return_val_if_fail (error == NULL || *error == NULL, FALSE);
 
   task = G_TASK (result);