LibWeb: Mark a BC's navigable as destroyed if it does not exist

Userland/Libraries/LibWeb/HTML/BrowsingContext.cpp

@@ -507,7 +507,7 @@ SandboxingFlagSet determine_the_creation_sandboxing_flags(BrowsingContext const&
 bool BrowsingContext::has_navigable_been_destroyed() const
 {
     auto navigable = active_document()->navigable();
-    return navigable && navigable->has_been_destroyed();
+    return !navigable || navigable->has_been_destroyed();
 }
 
 }