Exception is thrown when adding a relative link

Steps to reproduce

When adding a relative link, for instance to a link Collection, an exception is thrown on the server when saving the link.

1. Add a new link to a link Collection.

2. Set is as an external link with value "/test".

Stack trace for exception:

 <h2>Stack trace:</h2><div><code><pre class="StackTrace">[UriFormatException: Invalid URI: The hostname could not be parsed.]
   at System.Uri.CreateThis(String uri, Boolean dontEscape, UriKind uriKind)
   at System.UriBuilder..ctor(String uri)
   at EPiServer.UrlBuilder.Init(String url)
   at EPiServer.Cms.Shell.UI.Rest.ContentQuery.GetContentByPermanentLinkQuery.GetContent(ContentQueryParameters parameters) in d:\BuildAgent\work\1e4daa701ee5a3cd\EPiServer.Cms.Shell.UI\UI\Rest\ContentQuery\GetContentByPermanentLinkQuery.cs:line 55
   at EPiServer.Cms.Shell.UI.Rest.ContentQuery.ContentQueryBase.ExecuteQuery(IQueryParameters parameters) in d:\BuildAgent\work\1e4daa701ee5a3cd\EPiServer.Cms.Shell.UI\UI\Rest\ContentQuery\ContentQueryBase.cs:line 69
   at EPiServer.Cms.Shell.UI.Rest.ContentStructureStore.Get(ContentReference id, String query, ContentReference referenceId, String[] typeIdentifiers, Nullable`1 allLanguages, IEnumerable`1 sortColumns, ItemRange range) in d:\BuildAgent\work\1e4daa701ee5a3cd\EPiServer.Cms.Shell.UI\UI\Rest\ContentStructureStore.cs:line 141
   at lambda_method(Closure , ControllerBase , Object[] )
   at System.Web.Mvc.ReflectedActionDescriptor.Execute(ControllerContext controllerContext, IDictionary`2 parameters)
   at System.Web.Mvc.ControllerActionInvoker.InvokeActionMethod(ControllerContext controllerContext, ActionDescriptor actionDescriptor, IDictionary`2 parameters)
   at System.Web.Mvc.ControllerActionInvoker.<>c__DisplayClass13.<InvokeActionMethodWithFilters>b__10()
   at System.Web.Mvc.ControllerActionInvoker.InvokeActionMethodFilter(IActionFilter filter, ActionExecutingContext preContext, Func`1 continuation)
   at System.Web.Mvc.ControllerActionInvoker.InvokeActionMethodFilter(IActionFilter filter, ActionExecutingContext preContext, Func`1 continuation)
   at System.Web.Mvc.ControllerActionInvoker.InvokeActionMethodWithFilters(ControllerContext controllerContext, IList`1 filters, ActionDescriptor actionDescriptor, IDictionary`2 parameters)
   at System.Web.Mvc.ControllerActionInvoker.InvokeAction(ControllerContext controllerContext, String actionName)
   at EPiServer.Shell.Services.Rest.RestControllerBase.ExecuteCore()
   at System.Web.Mvc.ControllerBase.Execute(RequestContext requestContext)
   at EPiServer.Shell.Services.Rest.RestHttpHandler.ProcessRequest(HttpContextBase httpContext)
   at System.Web.HttpApplication.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()
   at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)