Fix callbacks being replaced on topics with wildcards

[v-zhuravlev]

I had an issue with router.addRoute described here by fellow MQTT users: #336.
In my case, I have the client with subscriptions to #, topic1, topic2 with different callbacks set for each. Due to e.Value.(*route).match(topic) (https://github.com/eclipse/paho.mqtt.golang/blob/master/router.go#L102) , new route/subscription overrides previous route instead of creating new one and only last callback is working for all routes.

And in my app I expect:
If I publish something to topic1, I expect both callbacks for # and topic1 subscriptions to fire. Not just the last one.

[MattBrittan]

Making this change and not also changing deleteRoute has the potential to be confusing (not that the existing code is not already confusing!). As the pull requestly currently stands calling:

Subscribe("#", xxx)
Subscribe("topic1", yyy)
Unsubscribe("topic1")

Would leave the route for "topic1" in place (Unsubscribe will call deleteRoute("topic1") which will match on "#", remove that route and return). The broker will continue to send all data through but only the callback for topic1 will remain active (definitly not what is intended).

The behaviour of the code in master as it currently stands is just as confusing; the above would result in no routes. However as this is a potentially breaking change to Subscribe then I believe that Unsubscribe/deleteRoute should also be updated to match at the same time.

Go Playground demonstrating this.

[v-zhuravlev]

Thanks @MattBrittan for such great comment, changed deleteRoute as well.

[alsm]

Thanks for fixing this up.