fix: tail list being expected on when it should be empty

crates/aiken-lang/src/gen_uplc.rs

@@ -2129,11 +2129,10 @@ impl<'a> CodeGenerator<'a> {
                     format!("__tail_{}", self.id_gen.next())
                 };
 
+                if tail.is_some() {
                     self.expect_type(tipo, &mut tail_stack, &name, &mut IndexMap::new());
 
                     expect_list_stacks.push(tail_stack);
-
-                if tail.is_some() {
                     names.push(name);
                 }