repair: move check for existing transaction earlier Several benefits: * Gets close the comment describing it * Splits off unrelated comment about "backup" argument * Error checking is customarily done early * If we added an early return to the method, it would still consistently fail if there was an existing transaction (so we would find and fix that case quickly) One test needs updating with for this change, because we no longer create the backup bundle before we fail. I don't see much reason to create that backup bundle. If some command was adding content and then trying to strip it as well within the transaction, we would have a backup for the user, but the risk of that not being discovered in development seems very small.