fix list parsing edge case

[fans656]

Fix an incorrect list parsing (text merged) in situation like:

foo
- bar

table

which output:

<p>foo<br />
table</p>
<ul>
<li>bar</li>
</ul>

instead of:

<p>foo</p>
<ul>
<li>bar</li>
</ul>
<p>table</p>

The "table" is wrongly matched by BLOCK_HTML specification due to the use of _BLOCK_TAGS_PATTERN without parens.

All text begins with what's in BLOCK_TAGS will have this issue.