Fix the change with paragraph_dir initialization.

Fix the change with paragraph_dir initialization.

 src/bidi.c (bidi_init_it): Don't initialize paragraph_dir here, as
 some callers set that themselves.
 src/xdisp.c (Fcurrent_bidi_paragraph_direction): Initialize
 itb.paragraph_dir to NEUTRAL_DIR.  Fixes an occasional incorrect
 cursor motion with <left> and <right> arrow keys.