This places an unnecessary degree of importance on content that is considered to be secondary to that of questions and answers. When it comes down to it, comments are not designed to be permanent. Some might even go so far as to suggest that they are temporary in nature.
Thus, unlike a question or an answer, a comment does not need to be a shining example of your best work.
Mat says it best in this answer:
Just post a follow-up comment if you want to clear up something you said previously. Breaking the "comment thread" is not a big deal. If you have more involved discussions around a question or answer, use the chat feature.
Thus, if you have a typo in your comment, one that makes the comment unreadable or introduces the potential for misinterpretation, simply delete it and resubmit it.
In this answer, Sha Wiz Dow Ard suggests a few different ideas for cases where another user has an issue with their comment and also reiterates the points I've made:
If there is glaring error in your own comment, new or old, just delete it and maybe add new comment explaining the "gap" in the other comments. If the problem is with comment made by other user, flag it choosing the relevant reason. Enough flags (depends on the comment votes) will automatically delete the comment.
Also, it's clear that comments shouldn't contain information that is needed by future visitors. This should be incorporated into the post body with an edit.
In short, adding such a feature would place too much importance on something that is only designed to clarify a post with the intention of improving it. Therefore, you don't need to worry about your comments getting stuck with a typo. Hope this helps!