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.
switch (blockSource) {
        case BlockSource::NETWORK:
            if (header) {
                updateHeadersSyncProgressLabel();
                return;
            }
            progressBarLabel->setText(tr("Synchronizing with network..."));
            updateHeadersSyncProgressLabel();
            break;
        case BlockSource::DISK:
            if (header) {
                progressBarLabel->setText(tr("Indexing blocks on disk..."));
            } else {
                progressBarLabel->setText(tr("Processing blocks on disk..."));
            }
            break;
        case BlockSource::REINDEX:
            progressBarLabel->setText(tr("Reindexing blocks on disk..."));
            break;
        case BlockSource::NONE:
            if (header) {