repl: fix autocomplete while using .load

This makes sure that complete functions work as expected after using
the REPL's `.load` command.

It also fixes the corresponding test. So far the assertion where
swallowed and the test passed even though it should not have.

Fixes: https://github.com/nodejs/node/issues/28546
PR-URL: https://github.com/nodejs/node/pull/28608


Reviewed-By: Jiawen Geng <technicalcute@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Lance Ball <lball@redhat.com>
Reviewed-By: Anto Aravinth <anto.aravinth.cse@gmail.com>