Ignore empty stub dex jars

Some modules do not provide APIs for all API surfaces, e.g.
sdk-extensions does not provide any public APIs, only system and above.
That means that the public stub dex jars are empty of classes*.dex
files. This change prevents "hiddenapi list" from failing in that
situation.

Bug: 179354495
Test: - migrate packages/modules/SdkExtensions to use bootclasspath_fragment
      - add the fragment to the platform-bootclasspath
      m out/soong/hiddenapi/hiddenapi-flags.csv
      - the previous command will verify that the SdkExtensions' generated
        all-stubs.flags matches the subset of monolithic flags that overlap.
      - check the SdkExtensions' generated all-stubs.flags to make sure it is
        complete.
Merged-In: Ib2f18b5ba4adec21b783a274fda8a3b797609f35
Change-Id: Ib2f18b5ba4adec21b783a274fda8a3b797609f35
(cherry picked from commit 496b9b43c987a2d769d0c178ee1d88cd92da84d9)
1 file changed