patch 8.2.4719: ">" marker sometimes not displayed in the jumplist

Problem:    ">" marker sometimes not displayed in the jumplist.
Solution:   If the buffer no longer exists show "-invalid-". (Christian
            Brabandt, closes #10131, closes #10100)
diff --git a/runtime/doc/motion.txt b/runtime/doc/motion.txt
index 7946a13..ede5112 100644
--- a/runtime/doc/motion.txt
+++ b/runtime/doc/motion.txt
@@ -1077,6 +1077,9 @@
 in the current file (an indent is removed and a long line is truncated to fit
 in the window).
 
+The marker ">" indicates the current position in the jumplist.  It may not be
+shown when filtering the |:jump| command using |:filter|
+
 You are currently in line 1167.  If you then use the CTRL-O command, the
 cursor is put in line 1154.  This results in: