synchronizer: fix race in _on_address_status
synchronizer: fix race in _on_address_status

Triggering needs two consecutive scripthash status changes
in very quick succession. Client gets notification from server,
but then response to "blockchain.scripthash.get_history" will already contain
the changed-again history that has a different status.

20190627T101547.902638Z |     INFO | synchronizer.[default_wallet] | receiving history mwXtx49BCGAiy4tU1r7MBX5VVLWSdtasCL 1
20190627T101547.903262Z |     INFO | synchronizer.[default_wallet] | error: status mismatch: mwXtx49BCGAiy4tU1r7MBX5VVLWSdtasCL

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