Fix NPE in MarkerFollowingRouteActivity

[Chaoba]

Run monkey test in Ali cloud test platform and find the following error, this PR fix this crash.

java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.Class java.lang.Object.getClass()' on a null object reference
	at android.animation.PropertyValuesHolder.setObjectValues(PropertyValuesHolder.java:663)
	at android.animation.PropertyValuesHolder.ofObject(PropertyValuesHolder.java:406)
	at android.animation.ValueAnimator.setObjectValues(ValueAnimator.java:506)
	at android.animation.ValueAnimator.ofObject(ValueAnimator.java:417)
	at com.mapbox.mapboxandroiddemo.examples.labs.MarkerFollowingRouteActivity$2.run(MarkerFollowingRouteActivity.java:132)
	at android.os.Handler.handleCallback(Handler.java:873)
	at android.os.Handler.dispatchMessage(Handler.java:99)
	at android.os.Looper.loop(Looper.java:201)
	at android.app.ActivityThread.main(ActivityThread.java:6806)
	at java.lang.reflect.Method.invoke(Native Method)
	at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:547)
	at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:873)