Fix quoted insert with invalid byte input

[tompng]

quoted_insert timeout was 1000 times larger. (forgot to do .fdiv(1000))
Fix a bug that readline unexpedly end when quoted_insert timed out. (Avoid insert_raw_char char=nil and use '' instead when timed out)

Fix this bug:

$ LANG=C irb
irb(main):001> (input \C-v あ)
(irb hangs and exits after 500 second)

[ima1zumi]

LGTM!