actually initialize kcrash properly

Summary:
to successfully use kcrash when linking with as-needed (which is a default
flag on many linux distros) one also needs to call KCrash::initialize.

without this kcrash may not be available for most users.

https://markmail.org/thread/zv5pheijaze72bzs

Test Plan: builds; target linked to kcrash even when using --as-needed

Subscribers: kde-edu

Tags: #kde_edu

Differential Revision: https://phabricator.kde.org/D17066