The command `mongoc_database_command_simple` leaks memory, when passing in a reply object created by bson_new. This can easily be reproduced with a few lines on C code: https://gist.github.com/kamulos/92b9a270c9e6e36e512cfa43ec470c26

I found this in a Rust wrapper of libmongoc: https://github.com/appsignal/mongo-rust-driver/issues/70

The only cause I could find is that the `flags` are set to `BSON_FLAG_STATIC` in `bson_copy_to`. This prevents the pointer being freed in `bson_destroy`.