tags: patch

From emacs -Q, insert the following in *scratch*, and evaluate it
twice.

(with-current-buffer (get-buffer-create "foo")
  (erase-buffer)
  (insert (make-string 200 ?\n))
  (cursor-sensor-mode +1)
  (display-buffer (current-buffer)))

The second time an error is triggered, here is a backtrace:

Debugger entered--Lisp error: (args-out-of-range 0)
  get-char-property(0 cursor-sensor-functions)
  cursor-sensor--detect(#<window 9 on *Backtrace*>)
  run-hook-with-args(cursor-sensor--detect #<window 9 on *Backtrace*>)
  redisplay--pre-redisplay-functions((#<window 9 on *Backtrace*>))
  apply(redisplay--pre-redisplay-functions (#<window 9 on *Backtrace*>))
  #[128 "\300\301\"\210\300\302\"\207" [apply redisplay--pre-redisplay-functions ignore nil] 4 nil nil]((#<window 9 on *Backtrace*>))
  redisplay_internal\ \(C\ function\)()

cursor-sensor-mode is a new feature in Emacs 25, so I propose the
following patch for emacs-25: