kio_help: Fix crash in QCoreApplication when accessing help://.
A recent commit d428fc8e6447ede81f1e1911d0b66b39265672f3 removed old
custom crash handling code in favor of KCrash. But this actually adds a
dependency on there being a valid QCoreApplication object.
I took from the example of the similar kio_file to simply create the
QCoreApplication here.
BUG:399709
Differential Revision: https://phabricator.kde.org/D16189