Use special exception when failing because the SSLEngine was closed (#10783)

Motivation:

Sometimes it would be helpful to easily detect if an operation failed due the SSLEngine already be closed.

Modifications:

Add special exception that is used when the engine was closed

Result:

Easier to detect a failure caused by a closed exception

handler/src/main/java/io/netty/handler/ssl/SslClosedEngineException.java

@@ -0,0 +1,31 @@
+/*
+ * Copyright 2020 The Netty Project
+ *
+ * The Netty Project licenses this file to you under the Apache License,
+ * version 2.0 (the "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at:
+ *
+ *   https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+ * License for the specific language governing permissions and limitations
+ * under the License.
+ */
+package io.netty.handler.ssl;
+
+import javax.net.ssl.SSLException;
+
+/**
+ * {@link SSLException} which signals that the exception was caused by an {@link javax.net.ssl.SSLEngine} which was
+ * closed already.
+ */
+public final class SslClosedEngineException extends SSLException {
+
+    private static final long serialVersionUID = -5204207600474401904L;
+
+    public SslClosedEngineException(String reason) {
+        super(reason);
+    }
+}

handler/src/main/java/io/netty/handler/ssl/SslHandler.java

@@ -851,7 +851,7 @@ public class SslHandler extends ByteToMessageDecoder implements ChannelOutboundH
                     if (exception == null) {
                         exception = sslClosePromise.cause();
                         if (exception == null) {
-                            exception = new SSLException("SSLEngine closed already");
+                            exception = new SslClosedEngineException("SSLEngine closed already");
                         }
                     }
                     promise.tryFailure(exception);