Add null check to updateHasAboveClientLocked

The same-process check in updateHasAboveClientLocked (see aosp/2577299)
was missing a null check: service's ProcessRecord is not guaranteed to
be set, for example if the client unbinds before the process hosting the
service is even started.

Test: atest MockingOomAdjusterTests
Change-Id: I220d9d1309cfc33316308bf805f4e34a0806a35d
Merged-In: Iee5024b8f13771bc98a39a20e5f96a89a4c79b4e
Merged-In: Id5aee1323b9b3b254e19e8a4e189c1fa4f9d96ea