fix possible race condition

src/Misc/Player.cs

@@ -1276,12 +1276,17 @@ namespace mpvnet
             }
         }
 
+        static object LoadFolderLockObject = new object();
+
         public void LoadFolder()
         {
             if (!App.AutoLoadFolder || Control.ModifierKeys.HasFlag(Keys.Shift))
                 return;
 
             Thread.Sleep(1000);
+
+            lock (LoadFolderLockObject)
+            {
                 string path = GetPropertyString("path");
 
                 if (!File.Exists(path) || GetPropertyInt("playlist-count") != 1)
@@ -1312,6 +1317,7 @@ namespace mpvnet
                 if (index > 0)
                     CommandV("playlist-move", "0", (index + 1).ToString());
             }
+        }
 
         bool WasAviSynthLoaded;