Adjust reference disposal checks

Author: Quahu

src/Laylua.Tests/Tests/Library/Entities/LuaReferenceTests.cs

@@ -69,4 +69,18 @@ public void MainThreadReference_PushedToChildThreadStack_PushesReferenceToChildT
         Assert.That(Lua.Stack.Count, Is.Zero);
         Assert.That(thread.Stack.Count, Is.EqualTo(1));
     }
+
+    [Test]
+    public void MainThreadReference_MainThreadDisposed_InvalidatesReference()
+    {
+        // Arrange
+        var lua1 = CreateLua();
+        var reference = lua1.Evaluate<LuaTable>("return {}")!;
+
+        // Act
+        lua1.Dispose();
+
+        // Assert
+        Assert.That(() => reference.IsEmpty, Throws.TypeOf<ObjectDisposedException>().With.Property(nameof(ObjectDisposedException.ObjectName)).EqualTo(typeof(LuaTable).FullName));
+    }
 }

src/Laylua/Library/Entities/Reference/LuaReference.cs

@@ -36,7 +36,14 @@ internal int Reference
 
     internal virtual bool IsDisposed
     {
-        get => _reference == LUA_NOREF;
+        get
+        {
+            if (_reference is LUA_NOREF)
+                return true;
+
+            var thread = ThreadCore;
+            return thread == null || thread.MainThread.IsDisposed;
+        }
         set => _reference = value ? LUA_NOREF : LUA_REFNIL;
     }
 
@@ -58,7 +65,7 @@ private protected LuaReference()
             Lua.FromThread(thread).PushLeakedReference(_reference);
         }
 
-        if (Thread!.Marshaler.ReturnReference(this))
+        if (thread.Marshaler.ReturnReference(this))
         {
             GC.ReRegisterForFinalize(this);
         }

src/Laylua/Library/LuaMainThread.cs

@@ -11,6 +11,8 @@ internal sealed class LuaMainThread : LuaThread
 
     internal override LuaMarshaler Marshaler => _lua.Marshaler;
 
+    internal override bool IsDisposed => _lua.IsDisposed;
+
     private readonly Lua _lua;
 
     public LuaMainThread(Lua lua)