fix here provider, handling failed routes

[nurikk]

There are cases when here can't compute routes between points. And summary field is missing

The summary is included in the response only if route calculation succeeds.

https://developer.here.com/documentation/routing/dev_guide/topics/resource-type-route-matrix-entry.html

This causes KeyError

>           if "travelTime" in obj["summary"]:
E           KeyError: 'summary'

[nilsnolde]

great thanks!!