Fix NPE in onDestroy.

NPE can happen when calls are canceled immediately before incallservice
has a chance to respond.

Bug:17362107
Change-Id: I6bf318f5f7d89731b686a1523678a26764fa9bf3

telecomm/java/android/telecomm/InCallService.java

@@ -165,11 +165,13 @@ public abstract class InCallService extends Service {
 
     @Override
     public boolean onUnbind(Intent intent) {
-        Phone oldPhone = mPhone;
-        mPhone = null;
+        if (mPhone != null) {
+            Phone oldPhone = mPhone;
+            mPhone = null;
 
-        oldPhone.destroy();
-        onPhoneDestroyed(oldPhone);
+            oldPhone.destroy();
+            onPhoneDestroyed(oldPhone);
+        }
         return false;
     }