playback: check for init before applying state

Check if the playback state still has not been initialized once we
restore.

This prevents one from playing a song while the restore task is
on-going and then having it overwritten by the restored state.

app/src/main/java/org/oxycblt/auxio/playback/state/PlaybackStateManager.kt

@@ -363,7 +363,7 @@ class PlaybackStateManager private constructor() {
 
         synchronized(this) {
             val exists =
-                if (state != null) {
+                if (state != null && !isInitialized) {
                     // Continuing playback while also possibly doing drastic state updates is
                     // a bad idea, so pause.
                     isPlaying = false