Fixed bug in office2john.py

Removed an assert which was causing a error to be thrown on docx generated with office for the mac. Checked all of the sample non hashes on the [wiki](http://openwall.info/wiki/john/sample-non-hashes) and the same output was produced for all of them before and after the change.

Here's the file in question: 
http://ubuntuone.com/5xXslhIqY2sLWZVIpMKzbq