JS error: Uncaught TypeError: Cannot set property 'popups' of undefined

Version tagged 1.7.30. Latest version of Chrome, 71.0.3578.98.

This is due to `late_localize_scripts()` - currently you have

```php
echo 'window.pum_vars.popups = window.pum_popups;';
```

Shouldn't it be
```php
echo 'window.pum_vars = {}; window.pum_vars.popups = window.pum_popups;';
```

Doesn't seem to affect popup display though.