OF-477 Additional SASL fix related to PR 279

https://github.com/igniterealtime/Openfire/pull/279

src/java/org/jivesoftware/openfire/net/SASLAuthentication.java

@@ -343,10 +343,12 @@ public class SASLAuthentication {
                         if (ss != null) {
                             boolean ssComplete = ss.isComplete();
                             String response = doc.getTextTrim();
+                            if (response.length() > 0){
                                 if (!BASE64_ENCODED.matcher(response).matches()) {
                                     authenticationFailed(session, Failure.INCORRECT_ENCODING);
                                     return Status.failed;
                                 }
+                            }
                             try {
                                 if (ssComplete) {
                                     authenticationSuccessful(session, ss.getAuthorizationID(),