drop the first-play pre-buffering

It made no perceivable difference to the first-play hitch, so it only cost buffering
audio at launch that the user may never play. loadWindow prepares when it plays again,
and the two tests go back to their original assertions.

app/src/main/kotlin/com/subtracks/playback/PlaybackController.kt

@@ -705,8 +705,10 @@ class PlaybackController(
         updating = true
         player.setWindow(window.map { it.item.toQueueItem() }, startIndex, startPositionMs)
         updating = false
-        player.prepare()
-        if (autoplay) player.play()
+        if (autoplay) {
+            player.prepare()
+            player.play()
+        }
         refresh(position)
     }