Telephony: Fix force close issue

- mContext in SIMRecords class inherits from parent class
  IccRecords become null resulting in NPE issue when SIM
  cards removed/disposed;
- Add null check for mContext in getDisplayRule() of class
  SIMRecords.

Change-Id: I530dc7b09e96359a93d46d95f421bc3a8b1d2ea2
CRs-Fixed: 1057570