Hide/disable `Render Preview` if no chunks are loaded by default

[jackjt8]

I'm unsure if JavaFX allows us to hide/show/disable(grey out) tabs retroactively like this.

However I have noticed a number of new users are confused by the loading process. If we can hide the Render Preview while no chunks are currently loaded, or to show a tooltip on a greyed out tab (stating to select chunks an then click on load... or new scene...), this may greatly improve new user experience.

Of course, we could still have an option to keep the Render Preview enabled at all times in case anyone wishes it to be.

[Peregrine05]

There is this, though.

[jackjt8]

For some reason that doesn't always seem to show up and users are confused.

[Peregrine05]

~This might be a 2.5.0 snapshot-only feature. Let me check.~

It also appears in 2.4.3.

[leMaik]

We should not hide it, but just grey it out. If we hide it, users might not know that it is there. I actually like the helpful message we have now, maybe we should just ensure that it is always displayed.

[jackjt8]

Unable to reproduce