Re-allow icons that are not theme icon

Particularly concerned are .desktop files.

See also:
15baa936

BUG: 429113

src/kitemviews/kfileitemmodelrolesupdater.cpp

@@ -1058,7 +1058,7 @@ bool KFileItemModelRolesUpdater::applyResolvedRoles(int index, ResolveHint hint)
             data = rolesData(item);
         }
 
-        if (QIcon::hasThemeIcon(item.iconName())) {
+        if (!item.iconName().isEmpty()) {
             data.insert("iconName", item.iconName());
         }