NaN return value when finding the distance to the same point

[bleege]

With certain LatLng values (e.g. LatLng(40.71199035644531, -74.0081)) we are getting a NaN return value when finding the distance to the same point.

LatLng ll1 = new LatLng(40.71199035644531, -74.0081);
LatLng ll2 = new LatLng(40.71199035644531, -74.0081);
double distance = ll1.distanceTo(ll2); // distance: NaN

It appears that in this particular case the sum of t1, t2 & t3 equals 1.0000000000000002 instead of 1 which then causes Math.acos() to return NaN since its > 1.

    public double distanceTo(LatLng other) {

        final double a1 = MathConstants.DEG2RAD * this.latitude;
        final double a2 = MathConstants.DEG2RAD * this.longitude;
        final double b1 = MathConstants.DEG2RAD * other.getLatitude();
        final double b2 = MathConstants.DEG2RAD * other.getLongitude();

        final double cosa1 = Math.cos(a1);
        final double cosb1 = Math.cos(b1);

        final double t1 = cosa1 * Math.cos(a2) * cosb1 * Math.cos(b2);
        final double t2 = cosa1 * Math.sin(a2) * cosb1 * Math.sin(b2);
        final double t3 = Math.sin(a1) * Math.sin(b1);
        final double tt = Math.acos(t1 + t2 + t3);

        return GeoConstants.RADIUS_EARTH_METERS * tt;
    }

[tobrun]

I started with writing a testcase for this issue:

This resulted in following output:

[tobrun]

Updated code of distanceTo:

[tobrun]

This landed with 78bedff in release branch of 3.1.0 in #3537