dropdown_widget: Fix bug in disable_for_spectators

If `disable_for_spectators` is true, the widget text is greyed out
but the tippy instance is still delegated, causing it to appear
on click/enter.

This commit fixes that by not delegating tippy if the
`disable_for_spectators` is true.

This bug was surfaced when it was found that the
topic type filter in Recent conversations has disabled
styling for spectators, but a spectator could still click on it to
open the dropdown.

Fixes #30461

web/src/dropdown_widget.ts

@@ -179,6 +179,11 @@ export class DropdownWidget {
             );
             return;
         }
+
+        if (this.disable_for_spectators && page_params.is_spectator) {
+            return;
+        }
+
         this.instance = tippy.delegate(delegate_container, {
             ...popover_menus.default_popover_props,
             target: this.widget_selector,