Force newline after rendering the final View

If the final call to `View()` (after emitting `tea.Quit`) does not end with a newline it is immediately overwritten by the shell prompt or by any other output. This can be a bit surprising and it's hard to debug if you don't know what happens.

It can be avoided by appending a newline to the result of the final call to `View()` if this result is not empty.