Fix #1435 and #1436 by reverting 7f7bf304b0b43a1445e68c15ee6f6403c7ca5b9e

Different PooledByteBufs can have the reference to the same PooledChunk (and its ByteBuffer), so it's incorrect not to create a duplicate.

buffer/src/main/java/io/netty/buffer/PooledUnsafeDirectByteBuf.java

@@ -71,7 +71,7 @@ final class PooledUnsafeDirectByteBuf extends PooledByteBuf<ByteBuffer> {
 
     @Override
     protected ByteBuffer newInternalNioBuffer(ByteBuffer memory) {
-        return memory;
+        return memory.duplicate();
     }
 
     @Override