Ensure the RenderTexture reference is valid on threaded task completion (#2024)

Author: rh101

core/2d/RenderTexture.cpp

@@ -468,14 +468,14 @@ void RenderTexture::onSaveToFile(std::string filename, bool isRGBA, bool forceNo
         {
             if (forceNonPMA && image->hasPremultipliedAlpha())
             {
-                _director->getJobSystem()->enqueue([this, image, _filename, isRGBA, forceNonPMA]() {
+                _director->getJobSystem()->enqueue([self = RefPtr(this), image, _filename, isRGBA, forceNonPMA]() {
                     image->reversePremultipliedAlpha();
 
-                    Director::getInstance()->getScheduler()->runOnAxmolThread([this, image, _filename, isRGBA] {
+                    Director::getInstance()->getScheduler()->runOnAxmolThread([self, image, _filename, isRGBA] {
                         image->saveToFile(_filename, !isRGBA);
-                        if (_saveFileCallback)
+                        if (self->_saveFileCallback)
                         {
-                            _saveFileCallback(this, _filename);
+                            self->_saveFileCallback(self, _filename);
                         }
                     });
                 });