avalonia: actually setup Avalonia before starting (#1453)

In removing the Avalonia setup workaround in #1445 we forget to replace
the SetupWithLifetime call with just SetupWithoutStarting!

Author: mjcheetham

src/shared/Core/UI/AvaloniaUi.cs

@@ -81,7 +81,8 @@ public static Task ShowWindowAsync(Func<Window> windowFunc, object dataContext,
 #else
                         .UsePlatformDetect()
 #endif
-                        .LogToTrace();
+                        .LogToTrace()
+                        .SetupWithoutStarting();
 
                     appInitialized.Set();