(regexp-opt): Bind completion-regexp-list to nil.

lisp/emacs-lisp/regexp-opt.el

@@ -102,6 +102,7 @@ by \\=\\< and \\>."
     ;; Recurse on the sorted list.
     (let* ((max-lisp-eval-depth (* 1024 1024))
 	   (completion-ignore-case nil)
+	   (completion-regexp-list nil)
 	   (words (eq paren 'words))
 	   (open (cond ((stringp paren) paren) (paren "\\(")))
 	   (sorted-strings (sort (copy-sequence strings) 'string-lessp))