fakeservicemanager: Don't accept null binders for addService am: 5f6ded8825 am: 0ba22cbbe8

Original change: https://android-review.googlesource.com/c/platform/frameworks/native/+/2308644

Change-Id: I8ff7eeab48f6a8c87a5aa8cb5516dce5277e386d
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>