Convert old latin1 labels, Raise exception if json conversion fails.
Convert old latin1 labels, Raise exception if json conversion fails.

A couple of changes
1) Old electrum wallets seemed to save labels in latin1, when you call json.dumps on line 83/84 it fails silently, which causes the label import to fail. Whenever electrum saves, it then overwrites your default wallet with no labels - essentially deleting all your labels. The solution to this is iterating over all the labels for old wallets decoding anything that fails to unicode() as latin1, and then unicoding it :)

2) Failing to import data and then deleting it is bad. So I'm raising an exception to avoid data being lost.
cryptapus/electrum,imrehg/electrum,aasiutin/electrum,molecular/electrum,aasiutin/electrum,dashpay/electrum-dash,spesmilo/electrum,argentumproject/electrum-arg,wakiyamap/electrum-mona,pooler/electrum-ltc,asfin/electrum,wakiyamap/electrum-mona,fireduck64/electrum,FairCoinTeam/electrum-fair,fujicoin/electrum-fjc,digitalbitbox/electrum,argentumproject/electrum-arg,romanz/electrum,vertcoin/electrum-vtc,kyuupichan/electrum,fireduck64/electrum,lbryio/lbryum,argentumproject/electrum-arg,romanz/electrum,cryptapus/electrum-uno,cryptapus/electrum,fireduck64/electrum,procrasti/electrum,vertcoin/electrum-vtc,molecular/electrum,lbryio/lbryum,protonn/Electrum-Cash,kyuupichan/electrum,cryptapus/electrum-uno,cryptapus/electrum-myr,fyookball/electrum,fireduck64/electrum,FairCoinTeam/electrum-fair,pknight007/electrum-vtc,kyuupichan/electrum,cryptapus/electrum,dabura667/electrum,dashpay/electrum-dash,pooler/electrum-ltc,pknight007/electrum-vtc,vertcoin/electrum-vtc,asfin/electrum,vialectrum/vialectrum,procrasti/electrum,argentumproject/electrum-arg,romanz/electrum,aasiutin/electrum,spesmilo/electrum,procrasti/electrum,procrasti/electrum,protonn/Electrum-Cash,neocogent/electrum,dabura667/electrum,fyookball/electrum,asfin/electrum,spesmilo/electrum,neocogent/electrum,protonn/Electrum-Cash,pooler/electrum-ltc,cryptapus/electrum-uno,pknight007/electrum-vtc,imrehg/electrum,wakiyamap/electrum-mona,dashpay/electrum-dash,aasiutin/electrum,cryptapus/electrum-myr,fyookball/electrum,pooler/electrum-ltc,molecular/electrum,vertcoin/electrum-vtc,protonn/Electrum-Cash,digitalbitbox/electrum,fujicoin/electrum-fjc,dabura667/electrum,cryptapus/electrum-uno,fujicoin/electrum-fjc,wakiyamap/electrum-mona,imrehg/electrum,FairCoinTeam/electrum-fair,dashpay/electrum-dash,molecular/electrum,spesmilo/electrum,digitalbitbox/electrum,vialectrum/vialectrum,vialectrum/vialectrum,cryptapus/electrum-myr,neocogent/electrum,imrehg/electrum,pknight007/electrum-vtc,FairCoinTeam/electrum-fair,cryptapus/electrum-myr,digitalbitbox/electrum,dabura667/electrum