Avoid an NPE for KEY_CARRIER_NR_AVAILABILITIES_INT_ARRAY

Fix an NPE where if KEY_CARRIER_NR_AVAILABILITIES_INT_ARRAY a
missing check in ImsNrSaModeHandler would cause the phone process
to crash.

Bug: 322353174
Test: atest FrameworksTelephonyTests
Test: Telephony Sanity (voice, data, sms) on Fi
Change-Id: I8132b187cfff74d8fdb7f7b7f01487f4914c40f6