bug#49248: 28.0.50; read-from-minibuffer returns a window-live-p error when its original window is deleted

[martin rudalics <rudalics@gmx.at>]

 > Thanks Martin for quick answer and fix, yes it is now working.

Pushed to master now.  Apparently, exiting from the minibuffer may
select a frame no less than four times here:

#1 in read_minibuf_unwind
   if (!EQ (exp_MB_frame, saved_selected_frame)
       && !NILP (exp_MB_frame))
     do_switch_frame (exp_MB_frame, 0, 0, Qt); /* This also sets
					     minibuf_window */

#2 in read_minibuf_unwind
       else if (WINDOW_LIVE_P (calling_window))
	Fset_frame_selected_window (calling_frame, calling_window, Qnil);

#3 in read_minibuf_unwind
   /* Restore the selected frame. */
   if (!EQ (exp_MB_frame, saved_selected_frame)
       && !NILP (exp_MB_frame))
     do_switch_frame (saved_selected_frame, 0, 0, Qt);

#4 in read_minibuf
   if (FRAMEP (calling_frame)
       && FRAME_LIVE_P (XFRAME (calling_frame))
       && (!EQ (selected_frame, calling_frame)
	  || (WINDOW_LIVE_P (XFRAME (calling_frame)->minibuffer_window)
	      && !EQ (XWINDOW (XFRAME (calling_frame)->minibuffer_window)
		      ->frame,
		      calling_frame))))
     call2 (Qselect_frame_set_input_focus, calling_frame, Qnil);

These will confuse the hell out of any window manager (and of me).  Can
some knowledgeable soul tell us what all this code is supposed to do and
whether it could be refactored in some sane way?

Many thanks in advance, martin