bug#17823: 24.3.91; end-of-visual-line: incorrect behaviour with truncate-lines and a line-prefix

[Nicolas Richard <theonewiththeevillook@yahoo.fr>]

Hi,

from emacs -Q, run the following with M-:

(progn
  (insert (make-string 500 ?x))
  (column-number-mode) ;; just to see it. plays no role.
  (beginning-of-line)
  (setq line-prefix (make-string 10 ? ))
  (visual-line-mode)
  (toggle-truncate-lines 1))

then hit C-e (end-of-visual-line) a few times. After some hits, the
cursor doesn't move anymore, although it's not at the end of the line.
On my machine, it goes to column 70, then 100, then stops there even
when hitting C-e again.

I expect emacs to scroll horizontally instead (like it does when
line-prefix is nil).

-- 
Nicolas.