test: refactor test-repl-tab-complete

* Add check for `data` object in tab completion callback
* Replace `.indexOf()` with `.startsWith()` where appropriate

PR-URL: https://github.com/nodejs/node/pull/10879


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>