Fix error messages returned by (Put)GetObjectLegalHold (#9013)

fiixing some minor discrepancies between aws s3 responses
vs minio server

pkg/bucket/object/lock/lock.go

@@ -475,6 +475,11 @@ type ObjectLegalHold struct {
 	Status  LegalHoldStatus `xml:"Status,omitempty"`
 }
 
+// IsEmpty returns true if struct is empty
+func (l *ObjectLegalHold) IsEmpty() bool {
+	return l.Status != ON && l.Status != OFF
+}
+
 // ParseObjectLegalHold decodes the XML into ObjectLegalHold
 func ParseObjectLegalHold(reader io.Reader) (hold *ObjectLegalHold, err error) {
 	if err = xml.NewDecoder(reader).Decode(&hold); err != nil {