Keyguard: Avoid array index out of bounds exception

When change sim configuration from dual to single card,
SubscriptionManager.getActiveSubInfoList() may get dual sim SubInfoRecord.

Check the slotId whether it is out of the array bounds.

CRs-Fixed: 755524

Change-Id: Ib58fe691c68a9df8eb2d642bde6d5aaa094c4ef7