Don't spend time on txout ntfns when no listeners.
Don't spend time on txout ntfns when no listeners.

cqswxj2013/btcd,jimmysong/btcd,decred/dcrd,jrick/btcd,wallclockbuilder/btcd,ppcsuite/ppcd,Stash-Crypto/btcd,ppcsuite/ppcd-old,jongillham/btcd,1d4Nf6/btcd,tb00/btcd,jrick/btcd,sysbot/btcd,hectorj/btcd,ppcsuite/ppcd-old,soapboxsys/ombfullnode,wallclockbuilder/btcd,toddfries/btcd,Evil-Coin/Evil,soapboxsys/ombfullnode,glv2/ppcd,davecgh/btcd,stevenroose/btcd,Evil-Coin/Evil,cjepson/btcd,qchain/btcd,runeaune/btcd,FactomProject/btcd,mathiasrw/btcd,jrick/dcrd,BitGo/prova,BitGo/prova,ltcsuite/ltcd,Roasbeef/btcd,stevenroose/btcd,dajohi/btcd,Cleawing/btcd,runeaune/btcd,dajohi/btcd,CryptocurrencyCabal/htcd,jrick/dcrd,aakselrod/btcd,mathiasrw/btcd,dan-da/btcd,jimmysong/btcd,btcsuitereleases/btcd,jcmincke/dcrd,qchain/btcd,Roasbeef/btcd,dajohi/btcd,Dirbaio/btcd,jrick/btcd,1d4Nf6/btcd,danoctavian/btcd,davecgh/btcd,danoctavian/btcd,btcsuite/btcd,sysbot/btcd,Stash-Crypto/btcd,Dirbaio/btcd,jcmincke/dcrd,tb00/btcd,adiabat/btcd,dan-da/btcd,CryptocurrencyCabal/htcd,cjepson/btcd,ltcsuite/ltcd,pkothbauer/btcd,pkothbauer/btcd,Cleawing/btcd,btcsuitereleases/btcd,glv2/ppcd,ppcsuite/ppcd,adiabat/btcd,DanielKrawisz/btcd,hectorj/btcd,btcsuite/btcd,FactomProject/btcd,cqswxj2013/btcd,decred/dcrd,toddfries/btcd,jongillham/btcd,jcmincke/dcrd,Dirbaio/btcd,aakselrod/btcd,DanielKrawisz/btcd