RFR 8234377: new BitArray(0).toString() throws ArrayIndexOutOfBoundsException

[Weijun Wang]

Please take a review at

   http://cr.openjdk.java.net/~weijun/8234377/webrev.00/

The BitArray::toString didn't expect the length could be zero and always tries 
to print out the last octet.

Thanks,
Max