fix sp lookup at genesis

[almogdepaz]

Purpose:

fix edge case looking up sps in genesis, we had a bug which mage us miss sps in the first slot
for the first slot we use None when looking up instead of looking for the slot to get the challenge we should use Genesis challenge, slot None only happens for the first slot in the chain

Current Behavior:

New Behavior:

Testing Notes:

[wjblanke]

aok

[coveralls-official]

Pull Request Test Coverage Report for Build 17646525702

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
• To avoid this issue with future PRs, see these Recommended CI Configurations.
• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 5 of 5 (100.0%) changed or added relevant lines in 2 files are covered.
• 160 unchanged lines in 16 files lost coverage.
• Overall coverage decreased (-0.1%) to 91.119%

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Files with Coverage Reduction	New Missed Lines	%
chia/daemon/client.py	1	74.16%
chia/daemon/keychain_proxy.py	1	70.57%
chia/daemon/server.py	1	83.54%
chia/farmer/farmer.py	1	73.32%
chia/full_node/full_node_store.py	1	92.93%
chia/introducer/introducer.py	1	81.9%
chia/timelord/timelord_api.py	1	93.02%
chia/timelord/timelord_launcher.py	2	89.29%
chia/_tests/simulation/test_simulation.py	3	96.47%
chia/introducer/introducer_api.py	5	81.48%

Totals
Change from base Build 17624749078:	-0.1%
Covered Lines:	102724
Relevant Lines:	112573

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💛 - Coveralls