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

src/com/android/settings/nfc/PaymentDefaultDialog.java

@@ -42,7 +42,11 @@ public final class PaymentDefaultDialog extends AlertActivity implements
     @Override
     protected void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
-        mBackend = new PaymentBackend(this);
+        try {
+            mBackend = new PaymentBackend(this);
+        } catch (NullPointerException e) {
+            finish();
+        }
         Intent intent = getIntent();
         ComponentName component = intent.getParcelableExtra(
                 CardEmulation.EXTRA_SERVICE_COMPONENT);