testnet no-snark-work fix

[deepthiskumar]

No snark work was being done until the first tree was filled. All the work returned by Parallel_scan.all_jobs is in a specific order and some trees weren't being included during the ordering process due to an off-by-one error.

Checklist:

• Tests were added for the new behavior
• All tests pass (CI will check this if you didn't)
• Serialized types are in stable-versioned modules
• Does this close issues? List them:

[bkase]

Great! Was going to ask for the test, but you’re way ahead of me.