Possible memory leak (find into_raw, but no from_raw)

[lucky1024]

As we known, we can use into_raw to transfer ownership of a string to a C caller. But we also need use from_raw to retake pointer to free memory.

into_raw/from_raw is a pair, but I only find into_raw in source code, and can not find from_raw. Failure to call from_raw will lead to a memory leak.

https://doc.rust-lang.org/std/ffi/struct.CString.html#method.into_raw