Fix an error when removing the entire map and the layers

Right now I get the following error when the map is destroyed within an Angular 1 application using ui-leaflet. This appears to be due to the controls being destroyed before the layers and thus no longer being around to be reset. This patch will fix that by adding some protection code around that logic. Here is the specific error I was running into:

angular.js:14642 TypeError: Cannot read property 'bottomright' of undefined
    at NewClass.onRemove (Leaflet.GoogleMutant.js:101)
    at NewClass.removeLayer (leaflet-src.js:6476)
    at NewClass.removeFrom (leaflet-src.js:6357)
    at NewClass.remove (leaflet-src.js:6350)
    at NewClass.remove (leaflet-src.js:3640)
    at eval (ui-leaflet.js:138)
    at Scope.$broadcast (angular.js:18698)
    at Scope.$destroy (angular.js:18313)
    at cleanupLastView (angular-ui-router.js:4083)
    at eval (angular-ui-router.js:4141)

changed the description

mentioned in issue #54 (closed)

I'm getting this issue as well, in Ember.js

This merge request fixes the issue for me. Will this be merged in anytime soon with a version release?

Thanks!

So this fixes #54 (closed), I guess?

Fix looks good to me.

merged

mentioned in commit fa28e955