Prevent index out of range

I3487634f1ec5bb3b5b60d636b64461d391add35a is causing build breakages in
unbundled builds.

The stubs libs are disabled for unbundled builds, and thus we shouldn't
declare them as dist artifacts.

Bug: 605033
Test: make -j dist ANDROID_BUILDSPEC=vendor/google/build/app_build_spec.mk
Change-Id: I3cd92e2cc6aeb48baf47d37780d8df2aa4756438