builder: Avoid reusing set GError
builder: Avoid reusing set GError

my_error was used twice, without clearing inbetween, which can
cause issues.

GeorgesStavracas/flatpak,handsome-feng/flatpak,handsome-feng/flatpak,flatpak/flatpak,amigadave/flatpak,GeorgesStavracas/flatpak,alexlarsson/xdg-app,amigadave/flatpak,flatpak/flatpak,matthiasclasen/xdg-app,GeorgesStavracas/flatpak,matthiasclasen/xdg-app,GeorgesStavracas/flatpak,amigadave/flatpak,flatpak/flatpak,handsome-feng/flatpak,amigadave/flatpak,matthiasclasen/flatpak,matthiasclasen/flatpak,flatpak/flatpak,handsome-feng/flatpak,GeorgesStavracas/flatpak,alexlarsson/xdg-app,matthiasclasen/xdg-app,handsome-feng/flatpak,alexlarsson/xdg-app,matthiasclasen/flatpak,matthiasclasen/xdg-app,matthiasclasen/flatpak,alexlarsson/xdg-app,matthiasclasen/flatpak,flatpak/flatpak