When isochrones layer is on, you can't click inside the layer to get another isochrone

[stevevance]

Problem: You cannot fetch a new isochrones layer from a click inside an existing isochrones layer.

Reproduce:

1. Get an isochrones layer for anywhere.
2. When the layer has loaded, click on one of the visualized areas of the isochrone.
3. Notice that you can't get another isochrone at the clicked location.
4. Click a part of the map outside the visualized area. A new isochrone layer will appear.