make llGetObjectPrimCount() return 0 on attachments, as spec

diff --git a/OpenSim/Region/ScriptEngine/Shared/Api/Implementation/LSL_Api.cs b/OpenSim/Region/ScriptEngine/Shared/Api/Implementation/LSL_Api.cs
index 66bad79..9b44199 100644
--- a/OpenSim/Region/ScriptEngine/Shared/Api/Implementation/LSL_Api.cs
+++ b/OpenSim/Region/ScriptEngine/Shared/Api/Implementation/LSL_Api.cs
@@ -14118,7 +14118,7 @@ namespace OpenSim.Region.ScriptEngine.Shared.Api
                 return 0;

             SceneObjectPart part = World.GetSceneObjectPart(id);
-            if (part == null)
+            if (part is null || part.ParentGroup.IsAttachment)
                 return 0;

             return part.ParentGroup.PrimCount;