lisp/frameset.el: Allow orphaned minibufferless frames.

lisp/frameset.el: Allow orphaned minibufferless frames.
(frameset-filter-minibuffer): Deal with the case that the minibuffer
parameter was already set in FILTERED.  Doc fix.
(frameset--record-minibuffer-relationships): Allow saving a
minibufferless frame without its corresponding minibuffer frame.
(frameset--reuse-frame): Accept a match from an orphaned minibufferless
frame, if the frame id matches.
(frameset--minibufferless-last-p): Sort non-orphaned minibufferless
frames before orphaned ones.
(frameset-restore): Warn about orphaned windows, instead of error out.