`clojure-sexp-starts-until-position` can loop forever

[vemv]

Per https://github.com/clojure-emacs/clojure-mode/pull/651/files#r1224358671 :

If function clojure-sexp-starts-until-position is called directly, then yes, it will loop forever for any single form in buffer. But this bug is triggered without user doing anything (except for opening the buffer) only when there's just comment in buffer