ECDSA verification succeeds when it shouldn't

[Guido Vranken]

My fuzzer found this:

ecc curve: secp256r1
public key X:
4534198767316794591643245143622298809742628679895448054572722918996032022405
public key Y:
107839128084157537346759045080774377135290251058561962283882310383644151460337
cleartext: {0xff, 0xff, 0xff, 0xff, 0x00, 0x00, 0x00, 0x00, 0xff, 0xff,
0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
 0xbc, 0xe6, 0xfa, 0xad, 0xa7, 0x17, 0x9e, 0x84, 0xf3, 0xb9, 0xca, 0xc2,
0xfc, 0x63, 0x25, 0x51} (32 bytes)
signature R:
4534198767316794591643245143622298809742628679895448054572722918996032022405
signature S:
4534198767316794591643245143622298809742628679895448054572722918996032022405

where 'cleartext' is the data passed as-is (unhashed) to the verification
function.

gcry_pk_verify() returns GPG_ERR_NO_ERROR for these parameters but other
libraries return failure.
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