Fix an out of bounds write in purple_markup_linkify.

Review Request #781 — Created June 23, 2021 and submitted — Latest diff uploaded

Information

pidgin/pidgin
release-2.x.y
d284f5089e0c

Reviewers

This was found by Thomas Roth <code@stacksmashing.net>, Dominik Maier
<mail@dmnk.co>, and Fabian Freyer <mail@fabianfreyer.de>.

Compiled and ran the purple_markup_linkify_fuzzer from the google oss-fuzz project to verify the fix.