Fix #15384: summary.php XSS vulnerability in MantisBT 1.2.12 only

Roland Becker (MantisBT Developer) discovered a XSS vulnerability
introduced in MantisBT 1.2.12 with the display of category/project names
on the summary.php page.

A malicious MantisBT user holding privileged manager/administrator
permissions could create a category or project name that contains
JavaScript code. Any user visiting summary.php from that point on may
then be exposed to having the malicious JavaScript execute within their
browser environment.

The severity of this issue is limited by the need to hold privileged
manager/administrator permissions in order to modify category and
project names. However -- there are many use cases where MantisBT
installations can have hundreds of sub-projects, each managed by
different people/parties that can not or should not be fully trusted.

Refer to previous commits 3ca8a164 and 6ec3f693 to trace back the origin
of this vulnerability.