REnv uses obj->c as env link; no super

src/proc.c

@@ -70,6 +70,7 @@ mrb_proc_new_cfunc(mrb_state *mrb, mrb_func_t func)
   p = (struct RProc*)mrb_obj_alloc(mrb, MRB_TT_PROC, mrb->proc_class);
   p->body.func = func;
   p->flags |= MRB_PROC_CFUNC;
+  p->env = 0;
 
   return p;
 }