NfcTile: Don't create an error when editing tiles

Repro:
* Make sure no NfcTile is in your expanded QS (not tested what happens if
  it's there)
* Hit the Edit-button:

Error in handleSetListeningInternal
java.lang.IllegalArgumentException: Receiver not registered: com.android.systemui.qs.tiles.NfcTile$1@7c00b87
	at android.app.LoadedApk.forgetReceiverDispatcher(LoadedApk.java:1434)
	at android.app.ContextImpl.unregisterReceiver(ContextImpl.java:1543)
	at android.content.ContextWrapper.unregisterReceiver(ContextWrapper.java:664)
	at com.android.systemui.qs.tiles.NfcTile.handleSetListening(NfcTile.java:64)
	at com.android.systemui.qs.tileimpl.QSTileImpl.handleSetListeningInternal(QSTileImpl.java:371)
	at com.android.systemui.qs.tileimpl.QSTileImpl.access$700(QSTileImpl.java:80)
	at com.android.systemui.qs.tileimpl.QSTileImpl$H.handleMessage(QSTileImpl.java:496)
	at android.os.Handler.dispatchMessage(Handler.java:107)
	at android.os.Looper.loop(Looper.java:214)
	at android.os.HandlerThread.run(HandlerThread.java:67)

* Only register or unregister the receiver if we actually need to change
  registered-state
* Same code is in AirPlaneModeToggle.java, presumably was also added to
  prevent unnecessary registering/unregistering

Change-Id: I6cd8f9bffccb68596b736cc0a3a38e9c12b9c489