Fail to parse short bogus comments

[openandclose]

Even in prescan, abrupt-closing-of-empty-comment should be treated as normal comments.

for <!-->, the spec states rather explicitly.

The two 0x2D bytes can be the same as those in the '<!--' sequence.'

But I think it is also applied to <!--->.

A failure test example, just in case.
https://github.com/openandclose/html-encoding-sniffer/commit/03708654d72139af9e1e5a18ccb829fd19cf61f5

prescan:
https://html.spec.whatwg.org/multipage/parsing.html#prescan-a-byte-stream-to-determine-its-encoding
abrupt-closing-of-empty-comment:
https://html.spec.whatwg.org/multipage/parsing.html#parse-error-abrupt-closing-of-empty-comment