RFR [8054221] StringJoiner imlementation optimization

[Ivan Gerasimov]

>> But if we do that, I think we should optimize size == 0 as well, thus:
>>
>> if (addLen == 0 && size <= 1)
>>  return (size == 0) ? "" : elts[0];
> Yes, done.
>
Or we can just call compactElts() if addLenn == 0, so it will work for 
any size.

Updated the webrev at the same location:
http://cr.openjdk.java.net/~igerasim/8054221/1/webrev/

Sincerely yours,
Ivan