fix(travel-times): Report walk times correctly when the origin is walking distance from the destinat

When the destination is walking distance and walking is the best way to get there, report such.

Author: mattwigway

lib/get-surface.js

@@ -39,7 +39,8 @@ export default function getSurface ({origin, query, stopTreeCache, which}) {
       fill(travelTimesForDest, nonTransitTime)
       fill(waitTimesForDest, 255)
       fill(inVehicleTravelTimesForDest, 255)
-      fill(walkTimesForDest, 255)
+      fill(walkTimesForDest, nonTransitTime) // when the origin is within walking distance and
+        // walking is the fastest way to reach the destination, _everything_ is walk time
 
       for (let stopIdx = 0; stopIdx < nStops; stopIdx++) {
         // read the stop ID