8246632: StringConcatFactory::makeConcatWithConstants no longer throws NullPointerException when an unexpected constant is null

[Claes Redestad]

Hi,

JDK-8246152 triggered a failure in a JCK test that expects a NPE
rather than a StringConcatException. We can keep the old behavior,
while retaining most of performance by removing the now superfluous
Objects.requireNonNull calls from within the parse loop.

Also fixed an issue where we were accidentally producing the wrong
message in case of mismatching number of constants or arguments.

Bug:    https://bugs.openjdk.java.net/browse/JDK-8246632
Webrev: http://cr.openjdk.java.net/~redestad/8246632/open.01/

Testing: tier1

Thanks!

/Claes