The following code crash the VMs on various platforms.

  f _ Form extent: 10 at 10.
  f magnify: f boundingBox by: 0.5 smoothing: 0.

  The fix would be to check the arguments in the primitive.

  But more general question would be that what is the best
way to prevent this kind of VM crash.  If the arguments (or
other conditions) are only checked in Squeak code, there are
ways to crash VM like this.  On the other hand, if they are
checked in the primitives, it results in the error messages
that are hard to interpret.

  So, I second Tim's suggestion about primitive failure
notifications.  It would make the error messages of
primitives more informative and writing backup code easier.

  -- Yoshiki