RFR(XS) 8170981: Possible access to char array with negative index

[Schmidt, Lutz]

Hi,

may I please ask for reviews and sponsorship for this small fix in command
line flag printing?

Bug: https://bugs.openjdk.java.net/browse/JDK-8170981
webrev: http://cr.openjdk.java.net/~simonis/webrevs/2016/8170981

Thank you!
Lutz