Avoid onServiceDisconnected() for unbind Service

onServiceDisconnected() and unbindLocked() both
are responsible to make mRemoteInstanceas null,
so ensure that the service is not unbinded already
while calling onServiceDisconnected()

Fixes:111631529
Test: Build Successful and device Running.
Change-Id: I505d97e32c4e76f06a358850e91fe189bf02654c

services/print/java/com/android/server/print/RemotePrintSpooler.java

@@ -705,8 +705,10 @@ final class RemotePrintSpooler {
         @Override
         public void onServiceDisconnected(ComponentName name) {
             synchronized (mLock) {
-                clearClientLocked();
-                mRemoteInstance = null;
+                if (mRemoteInstance != null) {
+                    clearClientLocked();
+                    mRemoteInstance = null;
+                }
             }
         }
     }