Fix ServiceConnector failing unbind if not connected.

ServiceConnector does not call unbindService when requested to unbind if
the service isn't currently connected. This causes issues like leaving
zombie Trusted Hotword processes bound forever if the process is stopped
('restarted') immediately after being created (say if audio server
crashes twice in quick succession).

Fix: 223845998
Test: manual - locally comment out code that immediately connects the
 service, then `for i in {1..10}; do adb shell cmd voiceinteraction\
 restart-detection; done` - without fix results in an extra process
Change-Id: I6a8c01390130bcec9aff1460004343ca2b207031
Merged-in: I6a8c01390130bcec9aff1460004343ca2b207031
(cherry picked from commit 52e0dafc)