Fixed "Cannot read property 'length' of undefined" on unregister when ho...

On unregister function if host hasn't been added yet `this.routing[src.hostname]` returned undefined and the process crashed a couple of lines after on `for(i=0; i<routes.length; i++){`. I didn't know if i should add a test for this or if this didn't need a test, so I added it. 

Have been using the project a little and its awesome, thanks for building it. Also, I could donate time to add support for Redis backend if you tell me what you have in mind with it, I see that there is already a file for this.