Menu disappears when scrollbar is touched (when not searchable)

[pjm17971]

The fix for #397 doesn't seem to work for the case where the selector is not searchable (searchable=false). The menu vanishes when the scrollbar is touched.

[burtyish]

👍

[burtyish]

When the menu is not searchable, this code in handleMouseDown causes the menu to close:

// for the non-searchable select, close the dropdown when button is clicked
if (this.state.isOpen && !this.props.searchable) {
    this.setState({
        isOpen: false
    }, this._unbindCloseMenuIfClickedOutside);
    return;
}

https://github.com/JedWatson/react-select/blob/master/src/Select.js#L367-L372

The code is supposed to close an open non-searchable menu when the Select-control is clicked (see #211). The problem is that handleMouseDown is used for both the Select-control and the menu. So clicking on the scrollbar triggers this code in the handler, closing the menu.