Add fixes for SimulatedLocationProvider

Instead of determining whether or not to start the simulation based on
whether or not the job is null, instead, use the active state of the job
to determine whether or not to start the simulator. This allows the
SimulatedLocationProvider to be reused more than once, and also allows
for addListener to happen before setSimulatedRoute is called without
breaking the simulation.

android/core/src/main/java/com/stadiamaps/ferrostar/core/Location.kt

@@ -155,7 +155,7 @@ class SimulatedLocationProvider : LocationProvider {
   override fun addListener(listener: LocationUpdateListener, executor: Executor) {
     listeners.add(listener to executor)
 
-    if (simulationJob == null) {
+    if (simulationJob?.isActive != true) {
       simulationJob = scope.launch { startSimulation() }
     }
   }
@@ -172,7 +172,7 @@ class SimulatedLocationProvider : LocationProvider {
     simulationState = locationSimulationFromRoute(route, resampleDistance = 10.0)
     lastLocation = simulationState?.currentLocation
 
-    if (listeners.isNotEmpty() && simulationJob == null) {
+    if (listeners.isNotEmpty() && simulationJob?.isActive != true) {
       simulationJob = scope.launch { startSimulation() }
     }
   }