dont make ThermionFlutterTexture inherit from ThermionDartTexture

thermion_flutter/thermion_flutter/macos/Classes/ThermionFlutterTexture.swift

@@ -2,20 +2,24 @@ import Foundation
 import GLKit
 import FlutterMacOS
 
-public class ThermionFlutterTexture : ThermionDartTexture,  FlutterTexture {
+public class ThermionFlutterTexture : NSObject, FlutterTexture {
     
     var flutterTextureId: Int64 = -1
     var registry: FlutterTextureRegistry
+    var texture: ThermionDartTexture 
     
     init(registry:FlutterTextureRegistry, width:Int64, height:Int64) {
         self.registry = registry
-        super.init(width:width, height:height)    
+        self.texture = ThermionDartTexture(width:width, height: height)
+        super.init()
         self.flutterTextureId = registry.register(self)
-            
     }
     
     public func copyPixelBuffer() -> Unmanaged<CVPixelBuffer>? {
-        return Unmanaged.passRetained(pixelBuffer!);
+        if(self.texture.pixelBuffer == nil) {
+            return nil
+        }
+        return Unmanaged.passRetained(self.texture.pixelBuffer!);
     }
     
     public func onTextureUnregistered(_ texture:FlutterTexture) {
@@ -24,7 +28,7 @@ public class ThermionFlutterTexture : ThermionDartTexture,  FlutterTexture {
     
     public func destroy() {
         self.registry.unregisterTexture(self.flutterTextureId)
-        self.destroyTexture()
+        self.texture.destroyTexture()
     }
     
-}
+}