Use cached stringEnd on subsequent calls to getValueAsByteRef()

Author: jordan-powers

libs/x-content/impl/src/main/java/org/elasticsearch/xcontent/provider/json/ESUTF8StreamJsonParser.java

@@ -46,6 +46,9 @@ public ESUTF8StreamJsonParser(
      */
     public ESBytesRef getValueAsByteRef() throws IOException {
         if (_currToken == JsonToken.VALUE_STRING && _tokenIncomplete) {
+            if(stringEnd > 0) {
+                return new ESBytesRef(_inputBuffer, _inputPtr, stringEnd-1);
+            }
             return _finishAndReturnByteRef();
         }
         return null;