Use a static const bool to check if khelpcenter is available on thrlHandler from KGUIAddons sets a handler for help:/ urls, which opens
khelpcenter if it's available or falls back to opening the relevant page
system, so as not to check every time a module is opened.at docs.kde.org.
Depends on D27615
BUG: 400602
FIXED-IN: 5.18.1