Themes: Don't add android overlay if target is android

If basePackageName equals "android" we are already overlaying the
framework so there is no need to overlay it a second time.  This is
the case for the system's resources as well as cases where explicit
assets are being requested for a package, which could be the android
package.

Change-Id: I5c881e71bc4d733fc8dbd7f752874ba34ab50f69