Unnamed variable should use generated name

Expression:
```
.Lambda #Lambda1<System.Action`2[System.Object,System.Object]>(
    System.Object $obj,
    System.Object $value) {
    .Block(System.Int32 $var1) {
        $var1 = 0
    }
}
```
Expected:
```cs
// generate unique name for variable, e.g. $varN
(obj, value) => var $var1 = 0
```
Actual:
```cs
(obj, value) => var  = 0
```