Fixed #57: Incorrect EOF test in getMessages

[thomasvargiu]

It's possible to send a Logoff action. When this happens, Asterisk sends a response message and then close the connection. With this PR is possible to read the Logoff response message without throwing an exception if it's the last message and the connection is closed after that.

Also related to #121, because it's a good practice to send a logoff to disconnect, but sending it could throws an exception at this moment. This PR fix this.

Some little fixes on the code found debugging it.

[coveralls]

Coverage remained the same at 91.932% when pulling 6cbc707e0d6b3dc7dbb999c4204ed4a31f86b4e1 on thomasvargiu:hotfix/57-read-and-eof into 61e58601c08731f754d21f5077000e034492f587 on marcelog:master.