Entrypoint script wipes data dir

Hi there!

I've been hit with this multiple times today, and it was really confusing until I figured out the reason. So I would make a new blank node dir with a data dir for a fresh snapshot import; mkdir -p node/data. Then import the snapshot, all good. But as soon as I start the node after, my freshly imported data is wiped from disk 😳

Turns out line 60 in entrypoint.inc.sh thinks it's OK to just wipe the entire data dir if the alphanet_version file does not exist. A snapshot import does not create this file, so yeah - data gone 🙈

It would be great if the script could be a bit less intrucive and instead perhaps show a suitable error message and exit or something.

Thanks!

Best, Asbjørn