unattend.inf only allows to add RunOnce entries, which are in theory only executed on the first boot after installation.
For almost a decade, this worked anyway to start regtest.cmd again after a ReactOS crash, because the registry and thus the deletion of the RunOnce entry wasn't stored on disk in case of a crash.
Thanks to Sylvain for the hint!
As Explorer processes the Run key right after RunOnce and therefore picks up regtest.cmd a second time during the first boot, exit the script just after adding the Run key.
Otherwise, rosautotest.exe would be started twice, with catastrophic results.
By default, we still fallback to FAT if nothing asked, or if there
is an invalid input.
0 is FAT, 1 is BtrFS. This can be grown as soon as we add more IFS.
