fix websocket crash when seeking and nothing is playing

Author: topi314

LavalinkServer/src/main/java/lavalink/server/io/WebSocketHandler.kt

@@ -127,6 +127,10 @@ class WebSocketHandler(
 
     private fun seek(json: JSONObject) {
         val player = context.getPlayer(json.getLong("guildId"))
+        if (!player.isPlaying) {
+            log.warn("Can't seek when player is not playing anything")
+            return
+        }
         player.seekTo(json.getLong("position"))
         SocketServer.sendPlayerUpdate(context, player)
     }

LavalinkServer/src/main/java/lavalink/server/player/PlayerRestHandler.kt

@@ -121,7 +121,7 @@ class PlayerRestHandler(
         playerUpdate.position.takeIf { it.isPresent && !playerUpdate.encodedTrack.isPresent && !playerUpdate.identifier.isPresent }
             ?.let {
                 if (player.isPlaying) {
-                    player.seekTo(it)
+                    player.seekTo(it.value)
                     SocketServer.sendPlayerUpdate(context, player)
                 }
             }