Merge pull request #1149 from slingamn/issue1059_certfp

fix #1059

irc/nickserv.go

 			target, certfp = params[0], params[1]
 		} else if len(params) == 1 {
 			certfp = params[0]
+		} else if len(params) == 0 && verb == "add" && rb.session.certfp != "" {
+			certfp = rb.session.certfp // #1059
 		} else {
 			nsNotice(rb, client.t("Invalid parameters"))
 			return