Don't free memory you didn't have allocated yourself.

You should not free something you didn't have allocated.

If you really want to keep the `delete` here to have a shorter syntax to create a new `Client`, you should change its value to `nullptr`.
In this case, the `delete` operation will be safe.

We have created a library which uses `libjson-rpc-cpp`, but because we allocate a new object in memory, we should free it ourself, `libjson-rpc-cpp` should not do it for us.
https://github.com/mage/mage-sdk-cpp/pull/14