Closing a modal with no tabs in TabList results in an error

[kennethbruskiewicz]

When I attempt to close the Modal and there are no tabs open, because the user closes all tabs they have from the Modal, I get a TypeError: tab is undefined and the relevant stack being:

getTabNode
scrollToIndex
toggleModal

I know that this isn't a typical case because generally we disallow tabs to be closable if there is just one, but in my case I need to allow all tabs to be closable from any point in this component's use.

Otherwise, great component, saved my skin. :+1: