Path Details produces ArrayIndexOutOfBoundsException
There is a minor problem when reducing the size and if size is 0

```
 /route
java.lang.ArrayIndexOutOfBoundsException: -1
        at com.graphhopper.util.PointList.add(PointList.java:260)
        at com.graphhopper.util.PathMerger.doWork(PathMerger.java:119)
        at com.graphhopper.routing.template.ViaRoutingTemplate.isReady(ViaRoutingTemplate.java:155)
        at com.graphhopper.GraphHopper.calcPaths(GraphHopper.java:1072)
```