Make some tweaks

examples/test.lua

@@ -8,4 +8,4 @@ function test()
     return add(10)(15)
 end
 
-global c = print(test())
+local c = print(test())

src/vm.rs

@@ -282,12 +282,14 @@ impl ClosureRunner {
                         }
                         _ => {
                             dbg!(&value);
+                            if *ret_len > 0 {
                                 for i in 0..=(*ret_len - 2) {
                                     self.stack.insert(*func_reg + i, Value::Nil);
                                 }
                             }
                         }
                     }
+                }
                 Instruction::Close(_) => {}
                 Instruction::Closure(reg, protok) => {
                     let highest_upvalue = self