Fix for uninitialized JSRuntime

When we arrive from an External Page into a Page which has a NavigationManager and has a LocationChanging Event registered,
Server Side Blazor would crash because of the uninitialized JSRuntime, during prerendering

Author: MariovanZeist

src/Components/Server/src/Circuits/RemoteNavigationManager.cs

@@ -100,7 +100,7 @@ protected override void NavigateToCore(string uri, bool forceLoad)
         /// <inheritdoc />
         protected override void SetHasLocationChangingListeners(bool value)
         {
-            _jsRuntime.InvokeAsync<object>(Interop.SetHasLocationChangingListeners, value);
+            _jsRuntime?.InvokeAsync<object>(Interop.SetHasLocationChangingListeners, value);
         }
 
         private static class Log