bug#47669: Customize option setting with key should be more lenient

[scame]

>
> Since there can be several buttons on a single line, I think it makes
> sense to make just the buttons be interactive -- adding DWIM here would
> be potentially confusing, so I'm closing this bug report.

Looks like there can't be multiple buttons on a line, because the 
implementation puts a newline after every widget:

  https://github.com/emacs-mirror/emacs/blob/master/lisp/cus-edit.el#L1759

Check the

  (widget-insert "\n")

lines.