Avoid duplicates in the mod list

Plugin.ClientModLoader/ModInjector.cs

@@ -1,5 +1,4 @@
 using System.Reflection.Emit;
-using System.Runtime.CompilerServices;
 using HarmonyLib;
 using Sandbox.Definitions;
 using Sandbox.Engine.Networking;
@@ -94,10 +93,21 @@ internal static class ModInjector
     private static void AppendToList(ref List<MyObjectBuilder_Checkpoint.ModItem> mods)
     {
         // copy
-        mods = mods.ToList();
+        mods = [.. mods];
 
-        mods.AddRange(AdditionalFilledModItems.Count > 0
-            ? AdditionalFilledModItems
-            : Mods.Select(mod => new MyObjectBuilder_Checkpoint.ModItem(mod, "Steam")));
+        if (AdditionalFilledModItems.Count > 0)
+        {
+            mods.AddRange(AdditionalFilledModItems);
+            return;
+        }
+
+        foreach (var mod in Mods)
+        {
+            //avoid duplicates
+            if (mods.FindIndex(m => m.PublishedFileId == mod) != -1)
+                continue;
+
+            mods.Add(new MyObjectBuilder_Checkpoint.ModItem(mod, "Steam"));
+        }
     }
 }