SYNOPSIS
        void dangling_lfun_closure()

DESCRIPTION
        Handle a dangling lfun-closure.

        This is called when the gamedriver executes a closure using a
        vanished lfun, with previous_object() showing the originating
        object. A proper handling is to raise a runtime error.

        Technical:
          Upon replacing programs (see efun replace_program()), any
          existing lambda closures of the object are adjusted to the
          new environment. If a closure uses a lfun which vanished in
          the replacement process, the reference to the lfun is
          replaced by an alien-lfun closure referencing to this function.
          The error will then occur when the execution of the adjusted lambda
          reaches the point of the lfun reference. There are two reasons for
          the delayed handling. First is that the program replacement and with
          it the closure adjustment happens at the end of a backend cycle,
          outside of any execution thread: noone would see the error at this
          time.  Second, smart closures might know/recognize the program
          replacement  and skip the call to the vanished lfun.

HISTORY
        Since LDMud 3.2.9, all references to dangling_lfun_closure() are
          created as alien-lfun closures.

SEE ALSO
        closures(LPC)
