openpgp: pass hash to Signer.Sign for ECDSA

Change-Id: Iabb601d9d7f3394c2a20cacd042c00bd05457500
Reviewed-on: https://go-review.googlesource.com/c/137897
Reviewed-by: Filippo Valsorda <filippo@golang.org>
Run-TryBot: Filippo Valsorda <filippo@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

openpgp/packet/signature.go

@@ -542,7 +542,7 @@ func (sig *Signature) Sign(h hash.Hash, priv *PrivateKey, config *Config) (err e
 			r, s, err = ecdsa.Sign(config.Random(), pk, digest)
 		} else {
 			var b []byte
-			b, err = priv.PrivateKey.(crypto.Signer).Sign(config.Random(), digest, nil)
+			b, err = priv.PrivateKey.(crypto.Signer).Sign(config.Random(), digest, sig.Hash)
 			if err == nil {
 				r, s, err = unwrapECDSASig(b)
 			}