JDK 9 RFR of 8059175: Zero BigDecimal with negative scale prints leading zeroes in String.format

[Brian Burkhalter]

Please review at your convenience.

Issue:  https://bugs.openjdk.java.net/browse/JDK-8059175
Patch:  http://cr.openjdk.java.net/~bpb/8059175/webrev.00/

In java.util.Formatter.BigDecimalLayout.layout() trailing zeroes are 
erroneously appended when the unscaled value of the BigDecimal is zero and the 
scale is negative. Some other minor changes are included to make the logic in 
the method clearer.

Thanks,

Brian