Allow listeners from a detached realm not to run

See whatwg/webidl#993.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

html/browsers/the-window-object/multiple-globals/window-open-no-browsing-context.html

diff --git a/html/browsers/the-window-object/multiple-globals/window-open-no-browsing-context.html b/html/browsers/the-window-object/multiple-globals/window-open-no-browsing-context.html
index 832e7bf..fe415ab 100644
--- a/html/browsers/the-window-object/multiple-globals/window-open-no-browsing-context.html
+++ b/html/browsers/the-window-object/multiple-globals/window-open-no-browsing-context.html
@@ -70,6 +70,11 @@
     });
     window.postMessage(token, '*');
   });
+  if (removed === 'entry' && !ran) {
+    // A listener from a realm that isn't fully active might not be invoked:
+    // https://github.com/whatwg/webidl/issues/993
+    return null;
+  }
   assert_true(ran, 'listener ran');
   if (error) {
     throw error;