RFR 8021863: Stream.concat incorrectly calculates unsized state

[Paul Sandoz]

Hi,

http://cr.openjdk.java.net/~psandoz/tl/JDK-8021863-concat-size/webrev/

This patch just tidies up calculating whether the concatenating spliterator is unsized or not before splitting. There was a typo when checking spliterator characteristics, but it turns out the characteristics do not need to be checked. Some tests are also added.

Paul.