add preconditons

lib/client/api.js

@@ -284,14 +284,12 @@ API.prototype.createAddress = function(cb) {
   var self = this;
 
   var data = this._loadAndCheck();
+  $.checkState(data.publicKeyRing.length != data.n, 'Wallet Incomplete, cannot derive address.');
 
   var url = '/v1/addresses/';
   this._doPostRequest(url, {}, data, function(err, address) {
     if (err) return cb(err);
 
-    if (data.publicKeyRing.length != data.n)
-      return cb('Wallet Incomplete, cannot derive address.')
-
     if (!Verifier.checkAddress(data, address)) {
       return cb(new ServerCompromisedError('Server sent fake address'));
     }