Fix SocketException in NioSocketChannelUnsafe.closeExecutor()

Related: #3464

Motivation:

When a connection attempt is failed,
NioSocketChannelUnsafe.closeExecutor() triggers a SocketException,
suppressing the channelUnregistered() event.

Modification:

Do not attempt to get SO_LINGER value when a socket is not open yet.

Result:

One less bug

transport/src/main/java/io/netty/channel/socket/nio/NioSocketChannel.java

@@ -332,7 +332,7 @@ public class NioSocketChannel extends AbstractNioByteChannel implements io.netty
     private final class NioSocketChannelUnsafe extends NioByteUnsafe {
         @Override
         protected Executor closeExecutor() {
-            if (config().getSoLinger() > 0) {
+            if (javaChannel().isOpen() && config().getSoLinger() > 0) {
                 return GlobalEventExecutor.INSTANCE;
             }
             return null;