[netty#5553] SimpleChannelPool#notifyConnect() may leak Channels

Motivation:

The SimpleChannelPool#notifyConnect() method will leak Channels if the user cancelled the Promise in between.

Modifications:

Release the channel if the Promise was complete before.

Result:

No more channel leaks.

transport/src/main/java/io/netty/channel/pool/SimpleChannelPool.java

@@ -154,9 +154,13 @@ public void run() {
         return promise;
     }
 
-    private static void notifyConnect(ChannelFuture future, Promise<Channel> promise) {
+    private void notifyConnect(ChannelFuture future, Promise<Channel> promise) {
         if (future.isSuccess()) {
-            promise.setSuccess(future.channel());
+            Channel channel = future.channel();
+            if (!promise.trySuccess(channel)) {
+                // Promise was completed in the meantime (like cancelled), just release the channel again
+                release(channel);
+            }
         } else {
             promise.setFailure(future.cause());
         }