fix(device_info_plus): Fix type cast of digitalProductId on windows

[konstantinullrich]

Description

This PR fixes a type cast error if digitalProductId does not exist.

[] as Uint8List causes the following error: type 'List<dynamic>' is not a subtype of type 'Uint8List' in type cast

Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I titled the PR using Conventional Commits.
• I did not modify the CHANGELOG.md nor the plugin version in pubspec.yaml files.
• All existing and new tests are passing.
• The analyzer (flutter analyze) does not report any problems on my PR.

Breaking Change

Does your PR require plugin users to manually update their apps to accommodate your change?

• Yes, this is a breaking change (please indicate that with a ! in the title as explained in Conventional Commits).
• No, this is not a breaking change.

[miquelbeltran]

LGTM! Thanks for the contribution!