Don't use invalid phone IDs as index.

phoneId can be -1 via this path, triggered via SimBootReceiver:
java.lang.Throwable
     at com.android.internal.telephony.dataconnection.DctController$SwitchInfo.<init>(DctController.java:743)
     at com.android.internal.telephony.dataconnection.DctController.setDefaultDataSubId(DctController.java:781)
     at com.android.internal.telephony.SubscriptionController.setDefaultDataSubId(SubscriptionController.java:1443)
     at com.android.internal.telephony.SubscriptionController.clearDefaultsForInactiveSubIds(SubscriptionController.java:1533)
     at com.android.internal.telephony.ISub$Stub.onTransact(ISub.java:307)
     at android.os.Binder.execTransact(Binder.java:446

Change-Id: Idf050fe5fff9b24cdbf890d0abc12d52fba21b3f