[fix] Dont allow async.forEach to be called on undefined or null arrays

lib/nconf/stores/redis.js

@@ -292,6 +292,7 @@ Redis.prototype.load = function (callback) {
       });
     }
     
+    keys = keys || [];
     async.forEach(keys, addValue, function (err) {
       return err ? callback(err) : callback(null, result);
     });
@@ -317,6 +318,7 @@ Redis.prototype.reset = function (callback) {
       return callback(err);
     }
     
+    existing = existing || [];
     async.forEach(existing, function (key, next) {
       self.clear(key, next);
     }, callback);