* doc/lispref/modes.texi (Imenu): Make it clear that sub-alist is the cdr.

* doc/lispref/modes.texi (Imenu): Make it clear that sub-alist is the cdr.

* lisp/imenu.el (imenu--subalist-p): Don't error on non-conses and
allow non-lambda lists as functions.
(imenu--in-alist): Don't recurse into non-subalists.
(imenu): Don't pass function itself as an argument.