Fixes QIcon::hasThemeIcon() behavior with our Icon Loader Engine
Fixes QIcon::hasThemeIcon() behavior with our Icon Loader Engine

It was always returning true.
Closes lxde/libqtxdg#98.
Closes lxde/lxqt#1081.
lxde/libqtxdg,libqtxdg/libqtxdg,lxde/libqtxdg,libqtxdg/libqtxdg,luis-pereira/libqtxdg,luis-pereira/libqtxdg