fix cd bug

stdlib/filesys.go

@@ -24,7 +24,15 @@ import (
 )
 
 func cd(in *ast.Token, vt ast.VarTable, ft ast.FuncTable) *ast.Token {
-    in = in.Eval(ft, vt, false)
+    in = in.Eval(ft, vt, true)
+
+    if in == nil {
+        log.Log(log.ERR,
+            "arguments to cd evaluated to nil!",
+            "cd")
+        return nil
+    }
+
     if in.Tag == ast.LIST {
         log.Log(log.ERR, "Couldnt change dir to a list", "cd")
         return nil