Correct pushGetMerkleBlock throttling.
Correct pushGetMerkleBlock throttling.

This commit corrects the check which sends in the done channel when
pushing merkle blocks that have no transactions to go with them.

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