org-latex--protect-texttt: Fix "---"

* lisp/ox-latex.el (org-latex--protect-texttt): Fix >2 consecutive
dashes.

Reported-by: Garid Zorigoo <garidzorigoo@gmail.com>
Link: https://orgmode.org/list/CAEDgBW44j4NpYUpppLpOA5Pmmsfi-GbCzDH4rTmRjf-F64mSaA@mail.gmail.com

lisp/ox-latex.el

@@ -1822,7 +1822,7 @@ INFO is a plist used as a communication channel.  See
           (replace-regexp-in-string
            "--\\|[\\{}$%&_#~^]"
            (lambda (m)
-             (cond ((equal m "--") "-{}-")
+             (cond ((equal m "--") "-{}-{}")
                    ((equal m "\\") "\\textbackslash{}")
                    ((equal m "~") "\\textasciitilde{}")
                    ((equal m "^") "\\textasciicircum{}")