Incorrect removal of debugger statement as dead code

``` js
var assert = function(x) {if (!x) {alert('c');debugger;}};
assert(prompt('a') === 'b');
```

is compiled to (in advanced mode)

``` js
if("b"!==prompt("a")){alert("c");debugger};
```

While

``` js
var assert = function(x) {if (!x) {debugger;}};
assert(prompt('a') === 'b');
```

is compiled to

``` js
prompt("a");
```

The former is the desired behaviour, at least in my case.