fix(dot/network): add nil checks in connManager (ChainSafe#2069)

Author: noot

dot/network/connmgr.go

@@ -130,7 +130,9 @@ func (cm *ConnManager) unprotectedPeers(peers []peer.ID) []peer.ID {
 func (cm *ConnManager) Connected(n network.Network, c network.Conn) {
 	logger.Tracef(
 		"Host %s connected to peer %s", n.LocalPeer(), c.RemotePeer())
-	cm.connectHandler(c.RemotePeer())
+	if cm.connectHandler != nil {
+		cm.connectHandler(c.RemotePeer())
+	}
 
 	cm.Lock()
 	defer cm.Unlock()
@@ -169,7 +171,9 @@ func (cm *ConnManager) Disconnected(_ network.Network, c network.Conn) {
 	logger.Tracef("Host %s disconnected from peer %s", c.LocalPeer(), c.RemotePeer())
 
 	cm.Unprotect(c.RemotePeer(), "")
-	cm.disconnectHandler(c.RemotePeer())
+	if cm.disconnectHandler != nil {
+		cm.disconnectHandler(c.RemotePeer())
+	}
 }
 
 // OpenedStream is called when a stream is opened