DNSSEC, assertion failed when creating DNSKEY from an ECDSA public key

Happens approximately in one case from a hundred.

lt-keymgr: lib/key/convert.c:162: int ecdsa_pubkey_to_rdata(gnutls_pubkey_t, dnssec_binary_t *): Assertion `point_x.size == point_y.size' failed.

The coordinates should be written aligned on a known fixed width without trimming the leading zeroes.