Please describe the problem:
GMimeFilterHTML, when used with the GMIME_FILTER_HTML_CONVERT_URLS flag, does not convert URLs with literal IPv6 addresses into hyperlinks. For example:

http://[2610:8:6800:1::7]/

This syntax is valid according to RFC 2732.

Steps to reproduce:
I wrote a test program that creates a GMimeFilterHTML with the GMIME_FILTER_HTML_CONVERT_URLS flag. I have that read in an text/plain email message which contains two URLs:

http://128.118.27.7/
and
http://[2610:8:6800:1::7]/

Actual results:
The first URL is converted into a hyperlink:
<a href="http://128.118.27.7/">http://128.118.27.7/</a>

The second URL is not.

Expected results:
Both URLs should be converted into hyperlinks. E.g.:

<a href="http://[2610:8:6800:1::7]/">http://[2610:8:6800:1::7]/</a>

Does this happen every time?
Yes

Other information:
This was tested with GMime 2.2.16.