Summary of Bug

In AnteHandler, FeeCollectionKeeper adds collected fees before saving signerAccs[0].
Attacker validator can send txs with fee and signerAccs[0] holding a false pubkey, ignoring the sig check error in CheckTx. Such txs will pass to DeliverTx, the FeeCollectionKeeper will collect fees, but these fees won't be charged from attacker's account due to sig check failure.

At gaia-9001 block 31998, we use this bug issue 150000 steaks.

@rigelrozanski

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