Allow locationFor(styleManager:) to optionally return location

[bsudekum]

Closes: #1511

This makes StyleManager.locationFor(styleManager:) allows developer to optionally return a location. The optionality we do in

mapbox-navigation-ios/MapboxNavigation/NavigationViewController.swift

Lines 611 to 621 in 96b2d6e

	public func locationFor(styleManager: StyleManager) -> CLLocation {
	guard let location = routeController.location else {
	if let coordinate = routeController.routeProgress.route.coordinates?.first {
	return CLLocation(latitude: coordinate.latitude, longitude: coordinate.longitude)
	} else {
	return CLLocation()
	}
	}
	return location
	}

doesn't seem to help us much in the case where routeController.location is nil.

/cc @mapbox/navigation-ios

[frederoni]

return routeController.location ?? routeController.routeProgress.route.coordinates?.first to make sure we have a location when we first apply day/night style? Should be safe to assume that the first coordinate on the route is in the same timezone as the user.

[JThramer]

Looks good!