feat(grunt): fail if files are missing

[Rotzbua]

• [x] Bugfix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)

Proposed changes

Build script should fail if source file is not available.

Reference

fixes #4738

Checklist

• [x] I have read the contribution guidelines
• [ ] For non-bugfix PRs, I have discussed this change on the forum/slack team.
• [ ] I have run npm run test to verify the unit tests pass
• [ ] I have added suitable unit tests to cover the new/changed functionality

[linux-foundation-easycla[bot]]

The committers listed above are authorized under a signed CLA.

• :white_check_mark: login: Rotzbua / name: Rotzbua (d115d6c241ab1a4a443e9e1d20ba59c0b546895d)