Fix fetch_last_token_balance function termination

[vbaranov]

Resolves #4934

Motivation

Fixing an error of kind:

2021-12-14T21:04:16.957 [error] GenServer #PID<0.735.406> terminating
** (Ecto.Query.CastError) apps/explorer/lib/explorer/chain/address/current_token_balance.ex:191: value `%{}` in `where` cannot be cast to type Explorer.Chain.Hash.Address in query:

from c0 in Explorer.Chain.Address.CurrentTokenBalance,
  where: c0.token_contract_address_hash == ^%Explorer.Chain.Hash{byte_count: 20, bytes: <<183, 211, 17, 226, 235, 85, 242, 246, 138, 148, 64, 218, 56, 231, 152, 146, 16, 185, 160, 94>>},
  where: c0.address_hash == ^%{},
  select: c0.value

    (elixir 1.12.2) lib/enum.ex:2385: Enum."-reduce/3-lists^foldl/2-0-"/3
    (elixir 1.12.2) lib/enum.ex:1704: Enum."-map_reduce/3-lists^mapfoldl/2-0-"/3
    (elixir 1.12.2) lib/enum.ex:1704: Enum."-map_reduce/3-lists^mapfoldl/2-0-"/3

Checklist for your Pull Request (PR)

• I added an entry to CHANGELOG.md with this PR
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• If I fixed a bug, I added a regression test to prevent the bug from silently reappearing again.
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