Update navigator.js

As described here: https://groups.google.com/d/msg/tiddlywikidev/AWvXz7RMIC4/gFF5crN2UJoJ

Providing a name for the new tiddler message only works if a skeleton tiddler already exists. If not, "New Tiddler" is taken. This change fixes that in that the provided name is taken even if there is no skeleton.