do_switch_frame: before leaving mini-window, check other (mru) window is live

This fixes bug#55684.  There, with a minibuffer-only frame at start up,
Emacs tried to switch to this frame, whose selected window was the
mini-window.  There is no other active window in this frame, so the
attempt to swith to another window failed.

* src/frame.c (do_switch_frame): On switching to a frame whose selected
window is as above, before selecting the most recently used window, check
this ostensible window is an actual live window.  Otherwise leave the
mini-window selected.

1 files changed, 7 insertions, 1 deletions

diff --git a/src/frame.c b/src/frame.c
index dc8045f41e6..0c278259a79 100644
--- a/src/frame.c
+++ b/src/frame.c
@@ -1568,8 +1568,14 @@ do_switch_frame (Lisp_Object frame, int track, int for_deletion, Lisp_Object nor
      to a different window, the most recently used one, unless there is a
      valid active minibuffer in the mini-window.  */
   if (EQ (f->selected_window, f->minibuffer_window)
+      /* The following test might fail if the mini-window contains a
+	 non-active minibuffer.  */
       && NILP (Fminibufferp (XWINDOW (f->minibuffer_window)->contents, Qt)))
-    Fset_frame_selected_window (frame, call1 (Qget_mru_window, frame), Qnil);
+    {
+      Lisp_Object w = call1 (Qget_mru_window, frame);
+      if (WINDOW_LIVE_P (w)) /* W can be nil in minibuffer-only frames.  */
+        Fset_frame_selected_window (frame, w, Qnil);
+    }
 
   Fselect_window (f->selected_window, norecord);