fix off-by-one error in execution code.

src/execute.mjs

@@ -11,7 +11,7 @@ export function execute (program, arg = id) {
 
 function call_fn (fn, env = []) {
 	if (typeof fn === "number") {
-		while (fn > 0) {
+		while (fn > 1) {
 			fn--;
 			env = env[1];
 		}