Fix CA1852

OpenRA.Game/Graphics/CursorManager.cs

@@ -17,7 +17,7 @@ namespace OpenRA.Graphics
 {
 	public sealed class CursorManager
 	{
-		class Cursor
+		sealed class Cursor
 		{
 			public string Name;
 			public int2 PaddedSize;

OpenRA.Game/Graphics/Model.cs

@@ -62,7 +62,7 @@ namespace OpenRA.Graphics
 	{
 		public Action<string> OnMissingModelError { get; set; }
 
-		class PlaceholderModelCache : IModelCache
+		sealed class PlaceholderModelCache : IModelCache
 		{
 			public IVertexBuffer<Vertex> VertexBuffer => throw new NotImplementedException();
 

OpenRA.Game/Graphics/Palette.cs

@@ -40,7 +40,7 @@ namespace OpenRA.Graphics
 			return new ReadOnlyPalette(palette);
 		}
 
-		class ReadOnlyPalette : IPalette
+		sealed class ReadOnlyPalette : IPalette
 		{
 			readonly IPalette palette;
 			public ReadOnlyPalette(IPalette palette) { this.palette = palette; }

OpenRA.Game/Graphics/SpriteFont.cs

@@ -427,7 +427,7 @@ namespace OpenRA.Graphics
 		}
 	}
 
-	class GlyphInfo
+	sealed class GlyphInfo
 	{
 		public float Advance;
 		public int2 Offset;