Error when setting a shortcut as external but it points to an internal media item

Steps to reproduce

1. Open a page and go to All Properties mode

2. Open the editor for the Shortcut.

3. Select "Shortcut to page on antother website"

4. Paste/Enter an url that points to a media item on this site

5. Click on the save button

Now you will get an http 500 error from the server.

Exception details: InvalidCastException: Unable to cast object of type 'EPiServer.Core.ContentReference' to type 'EPiServer.Core.PageReference'.

Stack trace:

[InvalidCastException: Unable to cast object of type 'EPiServer.Core.ContentReference' to type 'EPiServer.Core.PageReference'.]

at EPiServer.Cms.Shell.UI.ObjectEditing.InternalMetadata.ShortcutMetadataPropertyInfo.b__0(IContent content)

at EPiServer.Cms.Shell.UI.Rest.Models.Transforms.ContentDataModelBasePropertiesTransform.TransformInstance(IContent source, ContentDataStoreModel target, IModelTransformContext context)

at EPiServer.Cms.Shell.UI.Rest.Models.Transforms.TransformBase`1.d__0.MoveNext()

at System.Linq.Enumerable.WhereSelectEnumerableIterator`2.MoveNext()

at System.Linq.Enumerable.First[TSource](IEnumerable`1 source)

at EPiServer.Cms.Shell.UI.Rest.ContentDataStore.<>c__DisplayClass2.b__1(IContent content)

at EPiServer.Cms.Shell.UI.Rest.RestStatusUtil.ExecuteWithSecurityCheck[T](ContentReference contentLink, IContentRepository contentRepository, AccessLevel accessLevel, Func`2 func)

at EPiServer.Cms.Shell.UI.Rest.ContentDataStore.GetContent(ContentReference contentReference, DefaultQueryParameters queryParameters)

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__DisplayClass15.b__12()

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)