Don't bail on single-line definition list due to excess close tags.

Don't bail on single-line definition list due to excess close tags.

When parsing a single line definition list, we track nested tags so that:

	; <b>foo:bar</b>: baz

breaks before `baz`, not between `foo` and `bar`.  But we currently bail
out of this algorithm entirely if we see a mismatched close tag.  We should
just ignore the unmatched tag, like Parsoid does.

Change-Id: I6306dcad6347abeb6ab001d35562f1ab9f374bd1