`prism-whitespace-mode` freezes emacs when no space before line comment delimiters

Enabling `prism-whitespace-mode` in a buffer without spaces before line comment delimiter causes extreme slow downs. Here is an elisp example:

```
(defun my-delete-sentence (&optional arg);; <--- no space before ;; !!
(interactive "p")
(delete-region (point) (progn (forward-sentence arg) (point))))
(global-set-key (kbd "M-k") 'my-delete-sentence)

(defun my-delete-word (arg);; <--- no space before ;; !!
(interactive "p")
(delete-region (point) (progn (forward-word arg) (point))))
(global-set-key (kbd "M-d") 'my-delete-word)
```

(I'm not advocating for this style, but if you have enough students you will see all sorts of code.)