check if value is null in token balances refetch query

apps/explorer/lib/explorer/chain.ex

@@ -1496,7 +1496,7 @@ defmodule Explorer.Chain do
     query =
       from(
         balance in CoinBalance,
-        where: is_nil(balance.value_fetched_at) or is_nil(balance.value),
+        where: is_nil(balance.value_fetched_at),
         select: %{address_hash: balance.address_hash, block_number: balance.block_number}
       )
 

apps/explorer/lib/explorer/chain/address/token_balance.ex

@@ -82,7 +82,7 @@ defmodule Explorer.Chain.Address.TokenBalance do
       tb in TokenBalance,
       join: t in Token,
       on: tb.token_contract_address_hash == t.contract_address_hash,
-      where: is_nil(tb.value_fetched_at),
+      where: is_nil(tb.value_fetched_at) or is_nil(tb.value),
       where: (tb.address_hash != ^@burn_address_hash and t.type != "ERC-721") or t.type == "ERC-20"
     )
   end