Mutated variables in pseudo-block-scope loops aren't written back when using `continue`

For this code...

```
for (let i = 0; i < 5; i++) {
console.log(i++, [2].every(x => x != i))
continue
}
```

Bublé creates this:

```
var loop = function ( i$1 ) {
console.log(i$1++, [2].every(function (x) { return x != i$1; }))
return
};

for (var i = 0; i < 5; i++) loop( i );
```

It'd normally add an `i = i$1` to the end of the function, because it noticed that `i$1` is mutated, but for some reason it doesn't do that when the end of the loop isn't reachable. I originally observed a case where the assignment _was_ generated, but not reached because of a `continue` (compiled to a `return`).

In any case, this generated code produces different output than the original, because the mutations to `i` are dropped at the end of the loop body.

Start by reproducing the provided loop example and trace Bublé's pseudo-block-scope loop transformation, especially how `continue` becomes a `return`. The fix is done when mutations to `i` are written back and the transformed code preserves the original program's output.

Written by the indexing model from the issue text.