certificate chain validation error message is not returned

[JeyJeyGao]

The error message for validate certificate is not returned. Here is code.

notation-core-go/x509/cert_validations.go

Lines 91 to 94 in 0cb6e75

	func isIssuedBy(subject *x509.Certificate, issuer *x509.Certificate) bool {
	err := subject.CheckSignatureFrom(issuer)
	return err == nil && bytes.Equal(issuer.RawSubject, subject.RawIssuer)
	}

The subject.CheckSignatureFrom may return an error and the error message is not returned, which will finally cause an inaccurate error.

[patrickzheng200]

I will take this one and go through notation-core-go for similar issues.