net: don't send any messages before handshake or after fdisconnect
net: don't send any messages before handshake or after fdisconnect

Also, send reject messages earlier in SendMessages(), so that
disconnections are processed earlier.

These changes combined should ensure that no message is ever sent after
fDisconnect is set.

PIVX-Project/PIVX,PIVX-Project/PIVX,PIVX-Project/PIVX,Darknet-Crypto/Darknet,Darknet-Crypto/Darknet,PIVX-Project/PIVX,PIVX-Project/PIVX,PIVX-Project/PIVX,PIVX-Project/PIVX,Darknet-Crypto/Darknet,Darknet-Crypto/Darknet,PIVX-Project/PIVX,Darknet-Crypto/Darknet,PIVX-Project/PIVX,Darknet-Crypto/Darknet