[BUG] Empty string as display property

[Lars Hansen]

An empty string as display property has the advantage over the invisible
property that it can be made conditional. However, an empty string as
display property does not work. Try this:

(defun test ()
  (interactive)
  (select-window (display-buffer (get-buffer-create "*test*")))
  (erase-buffer)
  (insert "line 1\naaa"
          (propertize "bbb" 'display "")
          "ccc\nline 3"))

Maybe someone who knows the redisplay code would like to look at this bug.