Silent error when using a custom importer

[mosheKerbel]

When running node-sass with the default importer, an error would stop the process and return it with a failure.

{
  "status": 1,
  "file": "./src/files/textLn.scss",
  "line": 1,
  "column": 1,
  "message": "File to import not found or unreadable: ../../....",
  "formatted": "..."
}

But when using a custom importer, for example, node-sass-import-once Errors are not thrown, but silently written, so the process finishes and not stopped as expected.

It looks like this iteration over the importers is not handling the errors well: https://github.com/sass/node-sass/blob/886319b0c66af74145816fcc601ac0e7edbea1e9/lib/index.js#L320 I was unsure on how to handle it from here.