Add header tag if clientId is null

[anashalb]

If clientId is null during Portal Login, the header tag will not be added around LoginScopeHeader. The request therefore errors out.

[superfell]

Thanks for this, however i think a better fix would in ZKEnvelope to have the various writeHeader methods always call moveToHeaders.

[superfell]

Thanks for flagging this, i fixed it a slightly different way, and added a test in 04a2617

[anashalb]

Awesome, thanks for the fix