don't push twice for the same message to avoid race conditions

[ZabelTech]

What is the purpose of this pull request? (put an "X" next to item)

[ ] Documentation update [ x ] Bug fix [ ] New feature [ ] Other, please explain:

What changes did you make? (Give an overview) This PR changes Wire._message such that the entire binary data of a given message is pushed into the buffer at once.
This is necessary as pushing twice introduces a race condition which would produce malformed message. I saw that in practice and this change has fixed it.

Which issue (if any) does this pull request address?

Is there anything you'd like reviewers to focus on? ?? is widely available, but I'm not sure what backwards compatibility requirements this project has.