fix(alpine): exclude empty licenses for apk packages

[DmitriyLewen]

Description

After parsing line of apk package, we can get empty licenses.
e.g.:

"Licenses": [
            "",
            "Apache-2.0",
            "MIT",
            "",
            "MPL-2.0"
          ],

Related issues

• Close bug(apk): list of package license may contain empty strings #6128

Checklist

• I've read the guidelines for contributing to this repository.
• I've followed the conventions in the PR title.
• I've added tests that prove my fix is effective or that my feature works.
• I've updated the documentation with the relevant information (if needed).
• I've added usage information (if the PR introduces new options)
• I've included a "before" and "after" example to the description (if the PR is a user interface change).