[AI] Warning for invalid bounds on ANavLinkProxy

Using ANavLinkProxy's smart link but removing all of the simple links results in warnings in the logs for invalid bounds. The smart link is not set to be enabled until after the navigation element is created in PostRegisterAllComponents, but IsNavigationRelevant includes bSmartLinkIsRelevant prior to setting the SmartLinkComponent as navigation relevant. This causes the points of the smart link to not be used in creating the navigation bounds.

1. Add a NavLinkProxy actor to a level
2. Set SmartLink to be relevant, and set start/end points as desired
3. Remove all 'Simple Links' from the PointLinks array
4. Reload the level and the actor should generate warnings