URLs that start with underscores incorrectly disallowed

The 16 Jan 2013 patch to link.module does not apply to the latest link 7.x-1.x-dev and if still applicable needs a reroll.

error: while searching for:
  // Starting a parenthesis group with (?: means that it is grouped, but is not captured
  $protocol = '((?:'. implode("|", $allowed_protocols) .'):\/\/)';
  $authentication = "(?:(?:(?:[\w\.\-\+!$&'\(\)*\+,;=" . $LINK_ICHARS . "]|%[0-9a-f]{2})+(?::(?:[\w". $LINK_ICHARS ."\.\-\+%!$&'\(\)*\+,;=]|%[0-9a-f]{2})*)?)?@)";
  $domain = '(?:(?:[a-z0-9' . $LINK_ICHARS_DOMAIN . ']([a-z0-9'. $LINK_ICHARS_DOMAIN . '\-_\[\]])*)(\.(([a-z0-9' . $LINK_ICHARS_DOMAIN . '\-_\[\]])+\.)*('. LINK_DOMAINS .'|[a-z]{2}))?)';
  $ipv4 = '(?:[0-9]{1,3}(\.[0-9]{1,3}){3})';
  $ipv6 = '(?:[0-9a-fA-F]{1,4}(\:[0-9a-fA-F]{1,4}){7})';
  $port = '(?::([0-9]{1,5}))';

error: patch failed: link.module:1156
error: link.module: patch does not apply

I added a link in my content that starts with underscores and without applying a patch it is perfectly working in current version.

Last patch itself is wrong. I didn't see any pattern matching value is changed. Only variable name is made in caps format, which is wrong. Because that variables are not available.
Also that means without patch also functionality is already working fine. I'm totally agree with @sajid_007.

Can someone provide steps for how to reproduce the error?

Perhaps the URL validation should be expanded: https://stackoverflow.com/questions/161738/what-is-the-best-regular-expr...

When I tried to insert this link into my "Website" field with type "Link" I got an error:
The value https://_grisha.livejournal.com provided for Website is not a valid URL.
I'm using Link 7.x-1.7

@chegor: The patch hasn't been committed, this is an outstanding problem. And it needs test coverage.