scripts/functions: if no upstream URL is given, silently ignore that

When retrieving tarballs from upstream, if no URL was given, do not
fail; simmply ignore that fact.

This will be used later when the SVN helper will call the standard
helper to try the LAN mirror before trying svn.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

# Compute sparc-specific values

CT_DoArchTupleValues() {

    # That's the only thing to override

    if [ "${CT_ARCH_64}" = "y" ]; then

        CT_TARGET_ARCH="${CT_ARCH}64"

    fi

}