Avoid inflooping in redisplay caused by hscrolled R2L lines.

Avoid inflooping in redisplay caused by hscrolled R2L lines.

 src/xdisp.c (display_line): Don't assume that the call to
 reseat_at_next_visible_line_start ends up at a character
 immediately following the newline on the previous line.  Avoids
 setting the ends_at_zv_p flag on screen lines that are not at or
 beyond ZV, which causes infloop in redisplay.  For the details, see
 http://lists.gnu.org/archive/html/emacs-devel/2014-08/msg00368.html.