[reSIProcate] ServerInviteSession Bug on provisional

[Micky Kaufmann]

Hi,

There's an assertion if provisional is called when a UAS is in the
following states:
UAS_NoOfferReliable, UAS_EarlyReliable, UAS_FirstSentOfferReliable,
UAS_OfferReliable.

I don't see any reason for asserting these states.

This also means that there might be a bug in the state machine vsd
drawing (especially when new events are added without updating the
drawing)