[BUG] On-demand delta snapshot does not work when scheduled delta snapshotting is disabled

[shreyas-s-rao]

How to categorize this issue?

/area backup ops-productivity
/kind bug

What happened:
When I set delta-snapshot-period to 0 in order to disable scheduled delta snapshotting (support for which was added via #96 ), I am not able to trigger on-demand delta snapshots, which has nothing to do with scheduled delta snapshots.

What you expected to happen:
Expected on-demand delta snapshot to succeed.

How to reproduce it (as minimally and precisely as possible):
Run etcdbrctl in server mode an set CLI flag --delta-snapshot-period=0s. Then, once etcd and etcdbr are ready, call endpoint /snapshot/delta.

• etcd-backup-restore version: v0.40.0