If the QIconLoaderEngine (which respects theme and fallback theme) does not provide the icon, then try the QIconEngine provided by the QPlatformTheme implementation of createIconEngine. If that provides the requested icon, then use it; otherwise keep using an QIconLoaderEngine. Clean up the logic of that code a bit, while maintaining the invariant that we need to return a valid QIconEngine pointer. [ChangeLog][QtGui][QIcon] If neither theme nor fallback theme provide the requested icon, we fall back to the QPA plugin implementation. On platforms where an implementation exists, this will override the explicitly provided fallback (second parameter to QIcon::fromTheme). Change-Id: Idbf9ed049f5e975e1fbcdbb30dbdf6eac08e5827 Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>