Race condition when opening read capacitor before write capacitor is ready. 
The doc in fs-capacitor might be misleading, but [creating a WriteStream](https://github.com/jaydenseric/graphql-upload/blob/master/src/processRequest.mjs#L305) is actually [asynchronous](https://github.com/mike-marcacci/fs-capacitor/blob/v2.0.4/src/index.mjs#L142). 

Because we call [upload.resolve(file)](https://github.com/jaydenseric/graphql-upload/blob/master/src/processRequest.mjs#L351) before the fd is actually open, this could lead to issues like the one opened in [fs-capacitor](https://github.com/mike-marcacci/fs-capacitor/issues/18), where [path is set to an empty string](https://github.com/mike-marcacci/fs-capacitor/blob/v2.0.4/src/index.mjs#L77). 

