call secp256k1_start() with SECP256K1_START_VERIFY, otherwise, CPubKey::Verify() is called, which calls secp256k1_ecdsa_verify() and aborts on DEBUG_CHECK(secp256k1_ecmult_consts != NULL);
because secp256k1_start() didn't call secp256k1_ecmult_start(), which initializes secp256k1_ecmult_consts.