document-portal: Fix the document portal for files outside /app
document-portal: Fix the document portal for files outside /app

Strip /newroot prefix from document path since validate_parent_dir()
depends on a system path to get the parent directory stat.

GeorgesStavracas/flatpak,flatpak/flatpak,handsome-feng/flatpak,flatpak/flatpak,matthiasclasen/flatpak,GeorgesStavracas/flatpak,flatpak/flatpak,flatpak/flatpak,matthiasclasen/flatpak,matthiasclasen/flatpak,handsome-feng/flatpak,handsome-feng/flatpak,GeorgesStavracas/flatpak,GeorgesStavracas/flatpak,matthiasclasen/flatpak,flatpak/flatpak,GeorgesStavracas/flatpak,handsome-feng/flatpak,matthiasclasen/flatpak,handsome-feng/flatpak