Fix fresh node start with Snap sync failing

[nazar-pc]

Regression from recent object mappings changes. For regular node operation it doesn't matter if state exists, which it will not for parent of genesis block anyway since there can't be state for genesis block anyway.

Without this node with regular Snap sync (including Space Acres) fails like this:

Error: SubstrateService(Other("Failed to build a full subspace node 3: Sub(Client(Application("Missing state for mapping block 0 hash 0x6645…21bd: Api called for an unknown Block: Header was not found in the database: 0x0000000000000000000000000000000000000000000000000000000000000000, try a higher block number, or wipe your node and restart with --sync full")))"))

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[teor2345]

Thanks for fixing this, and sorry about the bug. I jumped too quickly from mappings to execution work.