SslHandlerTest#testCompositeBufSizeEstimationGuaranteesSynchronousWrite debug info

Motivation:
SslHandlerTest#testCompositeBufSizeEstimationGuaranteesSynchronousWrite has been observed to fail on CI servers. Knowing how many bytes were seen by the client would be helpful.

Modifications:
- Add bytesSeen to the exception if the client closes early.

Result:
More debug info available.

handler/src/test/java/io/netty/handler/ssl/SslHandlerTest.java

@@ -693,7 +693,8 @@ public class SslHandlerTest {
 
                                 @Override
                                 public void channelInactive(ChannelHandlerContext ctx) {
-                                    donePromise.tryFailure(new IllegalStateException("client closed"));
+                                    donePromise.tryFailure(new IllegalStateException("client closed. bytesSeen: " +
+                                                                                     bytesSeen));
                                 }
                             });
                         }