Noticed this while reviewing #13529, but it's also in master @ 5ba77df15. On macOS 10.13.6:

```
bitcoin-qt -disablewallet
```

<img width="1354" alt="schermafbeelding 2018-08-01 om 16 03 41" src="https://user-images.githubusercontent.com/10217/43526506-b23264d8-95a4-11e8-81a0-5debcad838ae.png">

The usual progress modal doesn't appear when QT starts, and clicking on the progress bar has no effect. It works fine when there's a wallet present.
#ifndef BITCOIN_QT_MODALOVERLAY_H
#define BITCOIN_QT_MODALOVERLAY_H
#include <QDateTime>
#include <QWidget>
static constexpr int HEADER_HEIGHT_DELTA_SYNC = 24;
namespace Ui {
    class ModalOverlay;