Load Qt translations even if some catalogs are missing

If loading the qt_ meta catalog fails (which may happen if loading fails for one of the four catalogs it depends on for most locales), then try loading the four catalogs separately. This is useful for AppImages and other packaging formats which may include only the catalogs of those Qt modules that are actually used.

I'm currently creating an AppImage for Kleopatra which uses qtbase, but neither qtscript nor qtmultimedia nor qtxmlpatterns. linuxdeploy (a tool for building AppImage) includes only the qt_ meta catalog and the qtbase catalog in the AppImage. This makes loading of the Qt translations fail for the AppImage although all necessary catalogs are available. With the proposed change loading of the Qt translations succeeds for the AppImage.