fix: Uses the correct index.

Author: bgrozev

src/main/java/org/ice4j/attribute/UsernameAttribute.java

@@ -81,7 +81,7 @@ void decodeAttributeBody(byte[] attributeValue, char offset, char length)
     {
         if (stripTrailingZeroes)
         {
-            while (length > 0 && attributeValue[offset + length] == 0)
+            while (length > 0 && attributeValue[offset + length - 1] == 0)
             {
                 length--;
             }