Fix vertical cursor motion from start of R2L lines in L2R paragraphs.

Fix vertical cursor motion from start of R2L lines in L2R paragraphs.

 src/xdisp.c (move_it_to): Don't bail out early when reaching
 position beyond to_charpos, if we are scanning backwards.
 (move_it_vertically_backward): When DY == 0, make sure we get to
 the first character in the line after the newline.