[nem-en] small fix for ants-icfp2004 snippet

[Marcin Grzeskowiak]

Hi,

After invoking `make run' in snippets/ants-icfp2004 ants.exe dies
with "unused goto assign to _N_945" error. The problem is caused
by UnfoldVars.n, line 46 (function scan_labels):
  vrs = v :: vars
After changing that line to
  vrs = v :: vrs
ants.exe runs without errors.

---
Marcin Grześkowiak

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