repl: do not save history for non-terminal repl

When running in non-TTY mode - the `repl.history` is `undefined` and
is not actually populated. Saving it will result in a crashes of
subsequent repl runs.

Fix: https://github.com/iojs/io.js/issues/1574
PR-URL: https://github.com/iojs/io.js/pull/1575


Reviewed-By: Chris Dickinson <christopher.s.dickinson@gmail.com>