Tolerate an empty android-extra-libs value

Skip the empty fields in the split. It's obvious that "" means nothing,
there's no other way to read the value.
It especially helps with machine-generated versions of the json files.

Change-Id: Idb957d4fa3076e908e5f437807b171f6ec56863c
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@theqtcompany.com>