null iv parameter passed to combo_init()

In contrib/pgcrypto/pgcrypto.c :

    err = px_combo_init(c, (uint8 *) VARDATA_ANY(key), klen, NULL, 0);

Note: NULL is passed as iv.

When combo_init() is called,

        if (ivlen > ivs)
            memcpy(ivbuf, iv, ivs);
        else
            memcpy(ivbuf, iv, ivlen);

It seems we need to consider the case of null being passed as iv for memcpy() because of this:

/usr/include/string.h:44:28: note: nonnull attribute specified here

What do you think of the following patch ?

Cheers