(telnet-filter): Position comint-last-output-start.

lisp/telnet.el

@@ -165,6 +165,7 @@ rejecting one login and prompting again for a username and password.")
 	   (ws (and w (window-start w))))
       (goto-char last-insertion)
       (insert-before-markers string)
+      (set-marker comint-last-output-start last-insertion)
       (set-marker (process-mark proc) (point))
       (if ws (set-window-start w ws t))
       (if ie (set-marker comint-last-input-end ie))