Fix license caching not properly checking fallback license url

[mikepenz]

• Fix issue causing fallback licenses not being fetched if a prior run did store the non fallback as checked in the remoteLicenseCache
  • FIX [Reproducibility issue] First-time build and subsequent builds don't produce the exact same "licenses" section #1085

[mikepenz]

If the cache includes the key because a url was checked before, we still wanna return null to ensure fallback fetching occurs:

• AboutLibraries/plugin-build/plugin/src/main/kotlin/com/mikepenz/aboutlibraries/plugin/util/LicenseUtil.kt

  Line 36 in 05e1f0f

  val singleLicense: String? = loadLicenseCached(enumLicense.getTxtUrl()) ?: loadLicenseCached(enumLicense.getFallbackTxtUrl())