RFR: JDK-8219480: j.l.c.ClassDesc::arrayType(int rank) throws IllegalArgumentException if rank = 0

[Vicente Romero]

Please review the simple patch to fix [1] at [2]. The patch is simply 
adding a comment to the API, (javadoc) to sync it with the implementation.

Thanks,
Vicente
[1] https://bugs.openjdk.java.net/browse/JDK-8219480
[2] http://cr.openjdk.java.net/~vromero/8219480/webrev.00/