RFR(JDK12/NIO) 8209576: java.nio.file.Files.writeString writes garbled UTF-16 instead of UTF-8

[Joe Wang]

Hi,

Please review a fix for a condition where a code conversion was skipped 
incorrectly resulting in a wrong byte array being written into the file.

JBS: https://bugs.openjdk.java.net/browse/JDK-8209576
webrevs: http://cr.openjdk.java.net/~joehw/jdk12/8209576/webrev/

Thanks,
Joe