go/neo/neonet: Fix segmentation violation in case handshake fails

Because 'err' was locally assigned inside the loop of 'DialLink' [1],
it was always 'nil' as a function return value, even when
'handshakeClient' actually returned an error. This lead to the
unfortunate situation that the function sometimes returned 'link=nil'
and 'err=nil', so that the function caller tried to access 'link'
attributes which lead to 'runtime error: invalid memory address or nil
pointer dereference'. This patch fixes this and now the function
correctly returns an error if the dialing fails.

[1] `peerConn, err := networker.Dial(ctx, addr)`

go/neo/neonet/newlink.go

@@ -319,9 +319,10 @@ func init() {
 
 // DialLink connects to address on given network, performs NEO protocol
 // handshake and wraps the connection as NodeLink.
-func DialLink(ctx context.Context, net xnet.Networker, addr string) (link *NodeLink, err error) {
+func DialLink(ctx context.Context, networker xnet.Networker, addr string) (link *NodeLink, err error) {
 	for _, enc := range dialEncTryOrder {
-		peerConn, err := net.Dial(ctx, addr)
+		var peerConn net.Conn
+		peerConn, err = networker.Dial(ctx, addr)
 		if err != nil {
 			return nil, err
 		}