Promise does not get rejected when the file or folder mentioned in loadPath does not exist

While opting the promise version of i18next and i18next-node-fs-backend, error does not get caught at the end of the chain when the file of folder mentioned in loadPath does not exist.

Start by reproducing the promise-based load with a missing file or folder in loadPath, then trace how the backend handles that failed filesystem lookup. Done means the promise is rejected and the error reaches the end of the chain for both missing files and folders.

Written by the indexing model from the issue text.