Incorrect minification of nested true if blocks

**Describe the bug**

Nested if blocks with true conditions are not minified correctly, not even close!

**To Reproduce**

Minimal code to reproduce the bug

```js
(function () {
let x = 1;
console.log(x);
if (true) {
let x = 2;
if (true) {
let x = 3;
console.log(x);
if (true) {
let x = 4;
console.log(x);
}
}
}
console.log(x);
})();
```

Console output:
```
1
3
4
1
```

**Actual Output**

```js
"use strict";
(function() {
var a = 1;
console.log(4);
console.log(a);
})();
```

Console output:
```
4
1
```
**Expected Output**

I don't really care much for what code would be outputted so, take this output with a pinch of salt.
What matters is that the console logs would give the same result.

```js
"use strict";
(function() {
var a = 1;
console.log(a);
console.log(3);
console.log(4);
console.log(a);
})();
```

**Configuration**

How are you using babel-minify?

I was using the Babel REPL and this bug appeared:
https://babeljs.io/en/repl#?babili=true&browsers=&build=&builtIns=false&spec=false&loose=false&code_lz=BQMwrgdgxgLglgewgAmASmQbwFDL8gGwFMZkAPZAXmQEYBuXfKJAZwWIDoCEBzYMtA3zI4IVDABOYIhhzC8xUhWoAmIfNHipMrI2EBIReSrIAzOrz7mENp258BFjWOCTpsvfn2GSx6gBYnb2tbIi5efkFPfQBfTzwY-WRPOOEQ9jD7SPUYtHQ6IA&debug=false&forceAllTransforms=false&shippedProposals=false&circleciRepo=&evaluate=false&fileSize=false&timeTravel=false&sourceType=script&lineWrap=true&presets=es2015%2Cbabili&prettier=true&targets=&version=6.26.0&envVersion=

Start with the minimal JavaScript example in the Babel REPL configuration linked in the issue, using the reported ES2015 and babili presets. Trace the minification of nested if blocks with true conditions and compare the transformed console sequence with the original. Done means the minified output preserves the 1, 3, 4, 1 logging order.

Written by the indexing model from the issue text.