selectedClass not being added with custom icon set
I'm using a custom icon set, which is a subset of Font Awesome 5, and contains both "regular" and "brand" icons, so I can't use `iconClass`. I'm initialising the iconpicker like this:

```
$("#my-iconpicker").iconpicker({
    footer: false,
    header: false,
    align: "left",
    cols: 12,
    icon: "",
    iconset: {
        iconClass: "",
        iconClassFix: "",
        icons: [
            "empty",
            "far fa-globe",
            "fab fa-windows",
            "fab fa-linux",
            "far fa-desktop",
            "far fa-server"
        ]
    },
    rows: 2,
    search: false,
    selectedClass: "btn-success",
    unselectedClass: ""
});
```

The problem is that when selecting an icon, the `btn-success` class isn't being added. Note that is _is_ added if the `empty` option is selected, so I believe it's related to there being spaces in the icon names.