Termination is simple.  Just call CloseIFF(iff).  This may be called at
any time, and terminates IFFParse's transaction with the stream.  The
stream itself is not closed.  The IFFHandle may be reused; you may safely
call OpenIFF() on it again.  You are responsible for closing the streams
you opened.  A stream used in an IFFHandle must generally remain open
until you CloseIFF().