Fix cursor motion in bidi-reordered continued lines.

Fix cursor motion in bidi-reordered continued lines.

 xdisp.c (try_cursor_movement): Backup to non-continuation line
 only after finding point's row.  Fix the logic.  Rewrite the loop
 over continuation lines in bidi-reordered buffers.  Return
 CURSOR_MOVEMENT_MUST_SCROLL upon failure to find a suitable row,
 rather than CURSOR_MOVEMENT_CANNOT_BE_USED.