JDK-8038451: Incorrect initialization order of static fields in sun.nio.cs.ext.JISAutoDetect$Decoder

[Mandy Chung]

This fixes the regression introduced by JDK-8038177 in which the osName 
field should be initialized before it's accessed in the class static 
initializer.

https://bugs.openjdk.java.net/browse/JDK-8038451

Webrev at:
http://cr.openjdk.java.net/~mchung/jdk9/webrevs/8038451/webrev.00/

Thanks
Mandy