virSecurityManagerNewStack: Don't ignore virSecurityStackAddNested retval

The virSecurityStackAddNested() can fail in which case
virSecurityManagerNewStack() should fail too.
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>
Reviewed-by: NJohn Ferlan <jferlan@redhat.com>

src/security/security_manager.c

@@ -117,9 +117,13 @@ virSecurityManagerNewStack(virSecurityManagerPtr primary)
     if (!mgr)
         return NULL;
 
-    virSecurityStackAddNested(mgr, primary);
+    if (virSecurityStackAddNested(mgr, primary) < 0)
+        goto error;
 
     return mgr;
+ error:
+    virObjectUnref(mgr);
+    return NULL;
 }