fix: escape unclosed tags without closing bracket in escape mode (#706)

[choi2601]

Summary

Fixed the issue where unclosed tags (e.g., <hello, <hello attr) resulted in an empty string when disallowedTagsMode is set to 'escape' or 'recursiveEscape'.

htmlparser2 drops malformed/unclosed tags at the end of the input stream without firing events. Added logic to check parser.endIndex after parsing completes to capture and escape any remaining unparsed content.

Closes #706

What are the specific steps to test this change?

1. Run the test suite: npm test
2. Verify the following cases manually or via tests:

#	Test	Input	Mode	Expected Output
1	Escape unclosed tag	<hello	escape	&lt;hello
2	Escape unclosed tag	<hello	recursiveEscape	&lt;hello
3	Escape unclosed tag with attributes	<hello you	escape	&lt;hello you
4	Escape unclosed tag with attributes	<hello you	recursiveEscape	&lt;hello you
5	Discard unclosed tag	<hello	discard	'' (empty)
6	Escape text + unclosed tag	Hello <world	escape	Hello &lt;world
7	Escape text + unclosed tag	Hello <world	recursiveEscape	Hello &lt;world

Result: All 190 tests passing (183 existing + 7 new)

What kind of change does this PR introduce?

(Check at least one)

• Bug fix
• New feature
• Refactor
• Documentation
• Build-related changes
• Other

Make sure the PR fulfills these requirements:

• It includes a) the existing issue ID being resolved, b) a convincing reason for adding this feature, or c) a clear description of the bug it resolves
• The changelog is updated
• Related documentation has been updated
• Related tests have been updated

Other information:

• Added 7 new test cases covering unclosed tags in escape, recursiveEscape, and discard modes
• Uses parser.endIndex (public API) from htmlparser2 to detect unparsed trailing content

[BoDonkey]

Thanks for this contribution. We will try to take a look and get back to you soon. However, could you update the CHANGELOG, please? Don't add a version number, just ## UNRELEASED and you change. Thanks!

[choi2601]

@BoDonkey
Thanks for the review! I've updated the CHANGELOG.md as requested.