fix: cancel CDN download tasks on dealloc to prevent use-after-free#410

mfazekas wants to merge 1 commit intorive-app:mainrive-app/rive-ios:mainfrom

mfazekas:fix/cdn-asset-loader-use-after-freemfazekas/rive-ios:fix/cdn-asset-loader-use-after-freeCopy head branch name to clipboard