wallet: fix balance_at_timestamp
wallet: fix balance_at_timestamp

closes #5326

vialectrum/vialectrum,neocogent/electrum,spesmilo/electrum,vialectrum/vialectrum,fujicoin/electrum-fjc,fujicoin/electrum-fjc,spesmilo/electrum,pooler/electrum-ltc,wakiyamap/electrum-mona,pooler/electrum-ltc,neocogent/electrum,spesmilo/electrum,spesmilo/electrum,wakiyamap/electrum-mona,pooler/electrum-ltc,vialectrum/vialectrum,pooler/electrum-ltc,fujicoin/electrum-fjc,wakiyamap/electrum-mona,wakiyamap/electrum-mona,neocogent/electrum