Fix ConnectionServiceFocusManager NPE

Bug: 294008627
Check for null Binder before calling focusmanager notification APIs

Bug: 294047434
Test: Unit Tests, OEM manual stress tests
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:c5ec887f5ec6d76a97c1598ea0c2bf3794b1dab1)
Merged-In: I62c6e6b75ab691ca8057f8151acacf6623fe53f9
Change-Id: I62c6e6b75ab691ca8057f8151acacf6623fe53f9