Avoid that unwind_format_mode_line messes up buffer points (Bug#32777)

* src/xdisp.c (format_mode_line_unwind_data): Before
temporarily selecting a window on another frame, separately save
the point of that window's buffer too.
(unwind_format_mode_line): After undoing the temporary
selection of a window on another frame, separately restore the
buffer point of that window.  This is needed since the
operation that deselects that window will have stored back the
point of that window into its buffer's point which is wrong
since that window was never "officially" selected (Bug#32777).

src/xdisp.c

@@ -11850,7 +11850,7 @@ format_mode_line_unwind_data (struct frame *target_frame,
   Vmode_line_unwind_vector = Qnil;
 
   if (NILP (vector))
-    vector = make_nil_vector (10);
+    vector = make_nil_vector (12);
 
   ASET (vector, 0, make_fixnum (mode_line_target));
   ASET (vector, 1, make_fixnum (MODE_LINE_NOPROP_LEN (0)));
@@ -11867,12 +11867,24 @@ format_mode_line_unwind_data (struct frame *target_frame,
   ASET (vector, 7, owin);
   if (target_frame)
     {
+      Lisp_Object buffer = XWINDOW (target_frame->selected_window)->contents;
+      struct buffer *b = XBUFFER (buffer);
+      struct buffer *cb = current_buffer;
+
       /* Similarly to `with-selected-window', if the operation selects
 	 a window on another frame, we must restore that frame's
 	 selected window, and (for a tty) the top-frame.  */
       ASET (vector, 8, target_frame->selected_window);
       if (FRAME_TERMCAP_P (target_frame))
 	ASET (vector, 9, FRAME_TTY (target_frame)->top_frame);
+
+      /* If we select a window on another frame, make sure that that
+	 selection does not leave its buffer's point modified when
+	 unwinding (Bug#32777).  */
+      ASET (vector, 10, buffer);
+      current_buffer = b;
+      ASET (vector, 11, build_marker (current_buffer, PT, PT_BYTE));
+      current_buffer = cb;
     }
 
   return vector;
@@ -11912,6 +11924,24 @@ unwind_format_mode_line (Lisp_Object vector)
 	}
 
       Fselect_window (old_window, Qt);
+
+      /* Restore point of target_frame_window's buffer (Bug#32777).
+	 But do this only after old_window has been reselected to
+	 avoid that the window point of target_frame_window moves.  */
+      if (!NILP (target_frame_window))
+	{
+	  Lisp_Object buffer = AREF (vector, 10);
+
+	  if (BUFFER_LIVE_P (XBUFFER (buffer)))
+	    {
+	      struct buffer *cb = current_buffer;
+
+	      current_buffer = XBUFFER (buffer);
+	      set_point_from_marker (AREF (vector, 11));
+	      ASET (vector, 11, Qnil);
+	      current_buffer = cb;
+	    }
+	}
     }
 
   if (!NILP (AREF (vector, 6)))