add support for EmptyQueryResponse

conn.go

@@ -652,6 +652,8 @@ func (c *Conn) processContextFreeMsg(t byte, r *msgReader) (err error) {
 		return c.rxErrorResponse(r)
 	case noticeResponse:
 		return nil
+	case emptyQueryResponse:
+		return nil
 	case notificationResponse:
 		c.rxNotificationResponse(r)
 		return nil

messages.go

@@ -21,6 +21,7 @@ const (
 	parameterDescription = 't'
 	bindComplete         = '2'
 	notificationResponse = 'A'
+	emptyQueryResponse   = 'I'
 	noData               = 'n'
 	closeComplete        = '3'
 	flush                = 'H'