KIconEngine: Return actual icon name of loaded icon
XDG icon themes return a "more generic" fallback icon if the
requested one cannot be found, e.g. foo-bar may return foo.
Previously, the returned QIcon would still return a name
of foo-bar, which made it impossible for applications to
check whether the specific icon requested was actually loaded.
Didn't want to add an overload or new method to the public API, so I shuffled some private parts and call them from the engine.
Edited by Kai Uwe Broulik