Steam beta update rolled out a fews days ago, it was only pushed to the general public today.
From the bugtracker thread, a Token return value is misdocumented in MSDN. ( "ReturnLength" is really hard-coded to
NULL while "PreviousState" is non-NULL (stack var))
Note that it is not the update process which is crashing, it is the post-install steam binary, part of the Steam client service.
Since it was a codeweavers employee that published the original patch, I'm certain they are aware. If it is like previous fixes a workaround will likely be posted in this thread/forum prior to issuing a general 13.0.1 update. (Purely speculation based on history, I am in no way involved with either codeweavers or wine)
EDIT: @Philip Law: The fix is not useless to you, as the same wine codebase is used to generate both the Mac and Linux versions of wine. Chances are they will both be fixed at around the same time.