media_player: Don't switch to first input source, if we actually know better. (#433)

* doubleCheck: Don't switch to zero, if we actually know better.

https://github.com/home-assistant/home-assistant/issues/9517

* Fix linting

* Reverting changes, introducing sourceIndexOld

src/more-infos/more-info-media_player.html

@@ -333,13 +333,14 @@ Polymer({
     this.callService('media_next_track');
   },
 
-  handleSourceChanged: function (sourceIndex) {
+  handleSourceChanged: function (sourceIndex, sourceIndexOld) {
     var sourceInput;
     // Selected Option will transition to '' before transitioning to new value
     if (!this.stateObj
         || this.stateObj.attributes.source_list === undefined
         || sourceIndex < 0
         || sourceIndex >= this.stateObj.attributes.source_list.length
+        || sourceIndexOld === undefined
     ) {
       return;
     }