Flush out test coverage for Message 1

[schwehr]

Looking at coverage for message1, the throw is the only line not covered. Need a message 1 that has a bad length. I know I've seen plenty in my logs, but need to either find one or make one up. And searching through many TB of logs isn't currently easy at the moment, crafting one would be easier. I'm currently having trouble with maven not doing a good job of showing me assert messages from junit, so it might take a bit.

if (six_state.bit_length() != 168)
    throw new AISMessageException("Message 1 wrong length"); // Untested line

And I realize that just hitting every line isn't enough, but it's a start.