[Bug-apl] Listing a function shouldn't create one

[Blake McBride]

Listing a non-existent function shouldn't create a new function.  This is a problem when you make a typo.

GNU APL:

      )CLEAR

CLEAR WS

      ∇GG[⎕]∇

    ∇

[0]   GG

    ∇

      )FNS

GG      

IBM APL 2:

      )CLEAR

CLEAR WS

      ∇GG[⎕]∇

DEFN ERROR

      )FNS

      ∇GG[⎕]

DEFN ERROR

      )FNS

      ∇GG

[1]   ∇

      )FNS

GG