[gnome-online-accounts] provider: Add 'error' precondition to goa_provider_get_all_finish()

[Debarshi Ray <debarshir src gnome org>]

commit e774891b40b282a2e29a8c3acf8a870e83bcfaa3
Author: Christophe Fergeau <cfergeau redhat com>
Date:   Sat Mar 26 12:43:31 2016 +0100

    provider: Add 'error' precondition to goa_provider_get_all_finish()
    
    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/goaprovider.c |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)
---
diff --git a/src/goabackend/goaprovider.c b/src/goabackend/goaprovider.c
index 6b82735..a98a17d 100644
--- a/src/goabackend/goaprovider.c
+++ b/src/goabackend/goaprovider.c
@@ -1231,6 +1231,7 @@ goa_provider_get_all_finish (GList        **out_providers,
 
   g_return_val_if_fail (g_simple_async_result_is_valid (result, NULL,
         goa_provider_get_all), FALSE);
+  g_return_val_if_fail (error == NULL || *error == NULL, FALSE);
 
   if (g_simple_async_result_propagate_error (simple, error))
     return FALSE;