Make sure clean task skips when there is nothing to clean

[liutikas]

Fixes #330

Test: Added a new test

[AbdulRehma4545]

FAILURE: Build failed with an exception.

• What went wrong:
  A problem was found with the configuration of task ':app:debugOssLicensesCleanUp' (type 'LicensesCleanUpTask').

  • In plugin 'com.google.android.gms.oss-licenses-plugin' type 'com.google.android.gms.oss.licenses.plugin.LicensesCleanUpTask' property 'generatedDirectory' specifies directory '/Users/.../app/build/generated/third_par.

    Reason: An input file was expected to be present but it doesn't exist.

    Possible solutions:

    1. Make sure the directory exists before the task is called.
    2. Make sure that the task which produces the directory is declared as an input.

    For more information, please refer to https://docs.gradle.org/8.13/userguide/validation_problems.html#input_file_does_not_exist in the Gradle documentation.