[9]RFR 6946830: javax.crypto.Cipher.doFinal behavior differs depending on platform

[Valerie Peng]

Anyone has time to review this trivial fix? This is a corner case of 
decrypting with 0-length data. Some provider throws exception but some 
just returns (no-op). For less impact, I changed all to match SunJCE 
provider's behavior which just returns.

Bug: https://bugs.openjdk.java.net/browse/JDK-6946830
Webrev: http://cr.openjdk.java.net/~valeriep/6946830/webrev.00/

Thanks,
Valerie