feat: check asar existence and integrity

[demetris-manikas]

No description provided.

[mention-bot]

By analyzing the blame information on this pull request, we identified @develar and @bontibon to be potential reviewers

[demetris-manikas]

Forgot to mention that this patch was created in response to #371.
Doesn't solve the problem but throws more descriptive errors.

[develar]

If we want to report more clear message if asar file doesn't exists, maybe we should fix code

try {
        return statFile(path.join(resourcesDir, "app.asar"), relativeFile) != null
      }
      catch (e) {
        // asar throws error on access to undefined object (info.link)
        return false
      }

? Here we just ignore error and returns false. I think, it is possible to throw error throw new Error(Package file ${asarFile} was not created.) here (checking error) and avoid yet another check.

[develar]

Is it real case?

[demetris-manikas]

#371 suggests that it is real. Haven't been able to reproduce.

[demetris-manikas]

Why not. It just feels more natural to me to first check for existence and then try to act on a file than trying to act on a file and on error check for its existence.

[develar]

Makes sense since #397 I feel that there is area to optimise, but... let's do it later.