Fixes Settings app crashing when NfcAdapter is null

If a device doesn't support NFC then
android.settings.NFCSHARING_SETTINGS and
android.nfc.cardemulation.action.ACTION_CHANGE_DEFAULT intents shouldn't
do anything and gracefully exit.

Test: Manual; Emulate a non-NFC device and test with apks sending intents
Bug: 80094104
Bug: 80092438
Change-Id: I5b3c3fdd582679e2cb16f474ef3331bc246b0d42