Only trigger a metadata sync if we don't have any cover artwork am: e085eb6f44 am: 4833c1bd65

Original change: https://googleplex-android-review.googlesource.com/c/platform/packages/apps/Bluetooth/+/11922314

Change-Id: I258ac10b2bbe906a36a5f512d9dcd07f62a4c47e