RFR: JDK-8057954 - IllegalStateException "combine message is empty" on attempt to end an I2C transaction

[alexey mironov]

issue: https://bugs.openjdk.java.net/browse/JDK-8057954
webrev: http://cr.openjdk.java.net/~alkonsta/8057954

Hi All,

Please review the changes made in order to fix issue with 
I2CCombinedMessage behavior.

Regards,
Alexey