Fix ClassCastException in HttpOperations#initShortId() (#3542)

Calling `HttpOperations#initShortId()` could cause a
`ClassCastException` if the underlying connection was replaced between
checking its type and casting it to `AtomicLong`, for example if
`ChannelOperations#terminate()` was called on another thread.

See also:
https://github.com/reactor/reactor-netty/blob/667f8c9cbf5a227a15f6d0a2f3aab7c4777613da/reactor-netty-core/src/main/java/reactor/netty/channel/ChannelOperations.java#L515

Fixes #3541

Co-authored-by: Violeta Georgieva <[email protected]>

reactor-netty-http/src/main/java/reactor/netty/http/HttpOperations.java

@@ -370,8 +370,9 @@ protected final boolean markSentHeaderAndBody(Object... objectsToRelease) {
 
 	@Override
 	protected final String initShortId() {
-		if (connection() instanceof AtomicLong) {
-			return channel().id().asShortText() + '-' + ((AtomicLong) connection()).incrementAndGet();
+		Connection connection = connection();
+		if (connection instanceof AtomicLong) {
+			return connection.channel().id().asShortText() + '-' + ((AtomicLong) connection).incrementAndGet();
 		}
 		return super.initShortId();
 	}