OMS: fix listener callbacks triggered by changes to target package

The OverlayManagerListener connected to the OverlayManagerServiceImpl
should be notified when and only when the overlay settings have been
modified. The pattern used to fulfill this contract as a result of a
change to a target package is as follows:

    if (updateAllOverlaysForTarget(...)) {
        mListener.onOverlaysChanged(...);
    }

Fix two violations of this pattern:

  - The listener was always notified
  - The listener was never notified

Test: manual
Change-Id: Id24a439e2eaaf976e8c7d650af36d58632cfb4ba