Fix inability to read user input after app exit

[matteodepalo]

There is a bug I introduced with https://github.com/vadimdemedes/ink/pull/616

If someone invokes render once with a component that uses useInput, then everything works fine (and that's why tests are passing). If instead you invoke render, wait for Ink to exit and then later in the execution you invoke it again with the same component, then node just quits because stdin has been dereferenced in the previous call to render.

With this PR I add a call to ref so that when the second call happens node stays up.

[vadimdemedes]

Thanks!