log: Avoid broken SELECTCOINS log
log: Avoid broken SELECTCOINS log

Before this patch, the log might be corrupted by other threads logging
at the same time. For example, another RPC thread:

[httpworker.1] [default wallet] keypool reserve 1296
[httpworker.1] SelectCoins() best subset: Received a POST request for / from 127.0.0.1:53732
[httpworker.3] ThreadRPCServer method=getnetworkinfo user=__cookie__
[httpworker.1] 0.78125 0.1953125 0.02441406 0.00610351 0.00305175 0.00152587 total 1.01025417

mm-s/bitcoin,particl/particl-core,instagibbs/bitcoin,jamesob/bitcoin,fanquake/bitcoin,pataquets/namecoin-core,domob1812/bitcoin,fanquake/bitcoin,bitcoinknots/bitcoin,achow101/bitcoin,achow101/bitcoin,jamesob/bitcoin,jambolo/bitcoin,anditto/bitcoin,bitcoinknots/bitcoin,mruddy/bitcoin,andreaskern/bitcoin,lateminer/bitcoin,sipsorcery/bitcoin,jambolo/bitcoin,pataquets/namecoin-core,GroestlCoin/bitcoin,fanquake/bitcoin,dscotese/bitcoin,bitcoinknots/bitcoin,bitcoinknots/bitcoin,kallewoof/bitcoin,bitcoin/bitcoin,jamesob/bitcoin,domob1812/bitcoin,jlopp/statoshi,AkioNak/bitcoin,GroestlCoin/bitcoin,andreaskern/bitcoin,sipsorcery/bitcoin,fujicoin/fujicoin,MarcoFalke/bitcoin,particl/particl-core,fujicoin/fujicoin,domob1812/bitcoin,fujicoin/fujicoin,prusnak/bitcoin,kallewoof/bitcoin,tecnovert/particl-core,particl/particl-core,prusnak/bitcoin,instagibbs/bitcoin,jamesob/bitcoin,domob1812/namecore,kallewoof/bitcoin,AkioNak/bitcoin,jambolo/bitcoin,ajtowns/bitcoin,fujicoin/fujicoin,namecoin/namecoin-core,GroestlCoin/GroestlCoin,sstone/bitcoin,domob1812/namecore,pataquets/namecoin-core,bitcoinsSG/bitcoin,particl/particl-core,Xekyo/bitcoin,GroestlCoin/GroestlCoin,dscotese/bitcoin,ajtowns/bitcoin,instagibbs/bitcoin,andreaskern/bitcoin,domob1812/bitcoin,bitcoin/bitcoin,Xekyo/bitcoin,bitcoinsSG/bitcoin,particl/particl-core,tecnovert/particl-core,tecnovert/particl-core,achow101/bitcoin,tecnovert/particl-core,namecoin/namecore,pataquets/namecoin-core,mm-s/bitcoin,GroestlCoin/bitcoin,ajtowns/bitcoin,namecoin/namecore,jambolo/bitcoin,fanquake/bitcoin,MarcoFalke/bitcoin,sipsorcery/bitcoin,domob1812/namecore,anditto/bitcoin,jlopp/statoshi,mm-s/bitcoin,namecoin/namecore,kallewoof/bitcoin,mruddy/bitcoin,lateminer/bitcoin,mm-s/bitcoin,andreaskern/bitcoin,bitcoinsSG/bitcoin,anditto/bitcoin,bitcoinknots/bitcoin,jamesob/bitcoin,sstone/bitcoin,bitcoin/bitcoin,fanquake/bitcoin,Xekyo/bitcoin,sipsorcery/bitcoin,ajtowns/bitcoin,achow101/bitcoin,bitcoinsSG/bitcoin,instagibbs/bitcoin,dscotese/bitcoin,mruddy/bitcoin,lateminer/bitcoin,jlopp/statoshi,namecoin/namecore,bitcoin/bitcoin,prusnak/bitcoin,fujicoin/fujicoin,GroestlCoin/GroestlCoin,anditto/bitcoin,achow101/bitcoin,jlopp/statoshi,namecoin/namecoin-core,sstone/bitcoin,prusnak/bitcoin,tecnovert/particl-core,Xekyo/bitcoin,anditto/bitcoin,dscotese/bitcoin,domob1812/namecore,namecoin/namecoin-core,GroestlCoin/bitcoin,MarcoFalke/bitcoin,fanquake/bitcoin,kallewoof/bitcoin,AkioNak/bitcoin,sipsorcery/bitcoin,domob1812/namecore,jlopp/statoshi,AkioNak/bitcoin,lateminer/bitcoin,lateminer/bitcoin,mm-s/bitcoin,prusnak/bitcoin,GroestlCoin/bitcoin,namecoin/namecore,bitcoin/bitcoin,dscotese/bitcoin,bitcoinsSG/bitcoin,MarcoFalke/bitcoin,Xekyo/bitcoin,Xekyo/bitcoin,fujicoin/fujicoin,jambolo/bitcoin,instagibbs/bitcoin,mruddy/bitcoin,jambolo/bitcoin,pataquets/namecoin-core,sstone/bitcoin,GroestlCoin/GroestlCoin,sipsorcery/bitcoin,mruddy/bitcoin,namecoin/namecoin-core,domob1812/bitcoin,sstone/bitcoin,MarcoFalke/bitcoin,pataquets/namecoin-core,dscotese/bitcoin,namecoin/namecore,andreaskern/bitcoin,kallewoof/bitcoin,GroestlCoin/GroestlCoin,lateminer/bitcoin,instagibbs/bitcoin,MarcoFalke/bitcoin,bitcoinsSG/bitcoin,particl/particl-core,tecnovert/particl-core,mm-s/bitcoin,jamesob/bitcoin,namecoin/namecoin-core,namecoin/namecoin-core,GroestlCoin/GroestlCoin,GroestlCoin/bitcoin,ajtowns/bitcoin,AkioNak/bitcoin,sstone/bitcoin,ajtowns/bitcoin,prusnak/bitcoin,andreaskern/bitcoin,bitcoin/bitcoin,achow101/bitcoin,mruddy/bitcoin,domob1812/bitcoin,domob1812/namecore,jlopp/statoshi,AkioNak/bitcoin,anditto/bitcoin