Refuse to run the Updater if the upgrade cycle hasn't finished

[joshtrichards]

In the web UI, when the "Go back to your Nextcloud instance to finish the update" comes up (which is supposed to be used to visit the instance and run the db migrations/app upgrades), it appears to be possible to merely hit reload and start the next update cycle.

This shouldn't be permitted.

Also, it's what turned up #566 in the wild (I think). Because the repair step (for the stray .step file we're leaving around) is added during the db migrations/etc.

This leaves the instance stuck in step 12 until manual intervention is taken.

This is currently possible because the Updater doesn't look at the database to check what version is currently in place, but merely looks at the version.php

Since we can't have the Updater connect to the db, we need a reliable mechanism for it to detect whether the upgrade cycle was fully completed.

[joshtrichards]

I guess is a funny sort of way, the .step file being left around after step 12 is an inadvertent clue that the db upgrades haven't been ran yet, since the repair steps not being ran is a good clue. So in a sense #566 is helping prevent the problem described in this issue.

But only until someone decides to manually remove the .step file themselves...

Then I think it becomes possible to update the code again, before running the prior migrations/repair steps/etc. Fairly certain that's not a good idea.