[libsecret] Fix secret_schema_unref detection of 0 refcount

[Christophe Fergeau <teuf src gnome org>]

commit 1b55291feb1e44977193989cf488e0dcd4bf518b
Author: Christophe Fergeau <cfergeau redhat com>
Date:   Sun Jul 26 22:36:20 2015 +0200

    Fix secret_schema_unref detection of 0 refcount
    
    g_atomic_int_add (&schema->refs, -1); will return the value of 'refs'
    _before_ adding -1 to it, so checking this value for 0 to see if the
    refcount dropped to 0 after adding -1 is not going to work and will
    cause a leak.
    Using g_atomic_int_dec_and_test() fixes this problem as this will return
    TRUE when the value drops to 0 after being decremented.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=756766

 libsecret/secret-schema.c |   12 ++++--------
 1 files changed, 4 insertions(+), 8 deletions(-)
---
diff --git a/libsecret/secret-schema.c b/libsecret/secret-schema.c
index 8bf7fa8..33522ef 100644
--- a/libsecret/secret-schema.c
+++ b/libsecret/secret-schema.c
@@ -355,16 +355,12 @@ _secret_schema_ref_if_nonstatic (const SecretSchema *schema)
 void
 secret_schema_unref (SecretSchema *schema)
 {
-       gint refs;
-       gint i;
-
        g_return_if_fail (schema != NULL);
+       /* statically-allocated or invalid SecretSchema */
+       g_return_if_fail (g_atomic_int_get (&schema->reserved) > 0);
 
-       refs = g_atomic_int_add (&schema->reserved, -1);
-       if (refs < 0) {
-               g_warning ("should not unreference a static or invalid SecretSchema");
-
-       } else if (refs == 0) {
+       if (g_atomic_int_dec_and_test (&schema->reserved)) {
+               gint i;
                g_free ((gpointer)schema->name);
                for (i = 0; i < G_N_ELEMENTS (schema->attributes); i++)
                        g_free ((gpointer)schema->attributes[i].name);