[#2589] LocalServerChannel.doClose() throws NPE when localAddress == null

Motivation:

LocalServerChannel.doClose() calls LocalChannelRegistry.unregister(localAddress); without check if localAddress is null and so produce a NPE when pass null the used ConcurrentHashMapV8

Modification:
Check for localAddress != null before try to remove it from Map. Also added a unit test which showed the stacktrace of the error.

Result:

No more NPE during doClose().

transport/src/main/java/io/netty/channel/local/LocalServerChannel.java

@@ -96,8 +96,10 @@ public class LocalServerChannel extends AbstractServerChannel {
     protected void doClose() throws Exception {
         if (state <= 1) {
             // Update all internal state before the closeFuture is notified.
+            if (localAddress != null) {
                 LocalChannelRegistry.unregister(localAddress);
                 localAddress = null;
+            }
             state = 2;
         }
     }

transport/src/test/java/io/netty/bootstrap/BootstrapTest.java

@@ -161,6 +161,32 @@ public class BootstrapTest {
         }
     }
 
+    @Test
+    public void testLateRegisterFailed() throws Exception {
+        final TestEventLoopGroup group = new TestEventLoopGroup();
+        try {
+            ServerBootstrap bootstrap = new ServerBootstrap();
+            bootstrap.group(group);
+            bootstrap.channel(LocalServerChannel.class);
+            bootstrap.childHandler(new DummyHandler());
+            bootstrap.localAddress(new LocalAddress("1"));
+            ChannelFuture future = bootstrap.bind();
+            Assert.assertFalse(future.isDone());
+            group.promise.setFailure(new IllegalStateException());
+            final BlockingQueue<Boolean> queue = new LinkedBlockingQueue<Boolean>();
+            future.addListener(new ChannelFutureListener() {
+                @Override
+                public void operationComplete(ChannelFuture future) throws Exception {
+                    queue.add(group.next().inEventLoop(Thread.currentThread()));
+                }
+            });
+            Assert.assertFalse(queue.take());
+        } finally {
+            group.shutdownGracefully();
+            group.terminationFuture().sync();
+        }
+    }
+
     private static final class TestEventLoopGroup extends DefaultEventLoopGroup {
         ChannelPromise promise;
         TestEventLoopGroup() {