Misleading guard statement in NavigationDirections.calculate(_:)

[JThramer]

mapbox-navigation-ios/MapboxCoreNavigation/OfflineDirections.swift

Lines 151 to 157 in 420b287

	NavigationDirectionsConstants.offlineSerialQueue.async { [weak self] in
	guard let result = self?.navigator.getRouteForDirectionsUri(url.absoluteString) else {
	let message = NSLocalizedString("OFFLINE_NO_RESULT", bundle: .mapboxCoreNavigation, value: "Unable to calculate the requested route while offline.", comment: "Error description when an offline route request returns no result")
	let error = OfflineRoutingError.unexpectedRouteResult(message)
	return completionHandler(nil, nil, error as NSError)
	}

Currently we're only returning the OFFLINE_NO_RESULT error if the directions client is improperly handled (self is nil when the asynchronous closure executes.) We should have a separate error for that, and actually check the result to ensure no error was returned from nav native.

/cc @mapbox/navigation-ios

[1ec5]

The suggestion is to break up the guard statement so that it only checks whether self (NavigationDirections) is still around; a let further down can call getRouteForDirectionsUri(_:).