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.
{
    if(!walletFrame)
        return false;
    return walletFrame->setCurrentWallet(name);
}
bool BitcoinGUI::setCurrentWalletBySelectorIndex(int index)
{
    QString internal_name = m_wallet_selector->itemData(index).toString();
    return setCurrentWallet(internal_name);
}
void BitcoinGUI::removeAllWallets()
{
    if(!walletFrame)
        return;
    setWalletActionsEnabled(false);
    walletFrame->removeAllWallets();
}
#endif 
void BitcoinGUI::setWalletActionsEnabled(bool enabled)