Don't error on 'C-h f menu-bar-open-mouse RET'

* lisp/help-fns.el (help-fns--insert-menu-bindings): Fix error when
passed 'menu-bar-open-mouse'.  (Bug#76172)

1 files changed, 2 insertions, 1 deletions

diff --git a/lisp/help-fns.el b/lisp/help-fns.el
index 9324cf85454..6112df99850 100644
--- a/lisp/help-fns.el
+++ b/lisp/help-fns.el
@@ -649,7 +649,8 @@ the C sources, too."
          (lambda (entry level)
            (when (symbolp map)
              (setq map (symbol-function map)))
-           (when-let* ((elem (assq entry (cdr map))))
+           (when-let* ((elem (assq entry (cdr map)))
+                       (_ (proper-list-p elem)))
              (when (> level 0)
                (push sep string))
              (if (eq (nth 1 elem) 'menu-item)