GPP Junk Padding Fix

So I came across a GPP password in Win2k8 test environment that appended Junk padding to the string. This may be what @carnal0wnage came across in http://carnal0wnage.attackresearch.com/2012/10/group-policy-preferences-and-getting.html

I tried to work out what was going on but it appears that the additional characters are junk and should be stripped. These characters did not occur on my Win2k8R2 machine. 

I have updated spec and the decryption code to be more robust when this occurs. I don't know the maximum amount of junk padding that could be appended but saw up to 6 chars in my testing.