f2fs: let's avoid panic if extent_tree is not created
This is an automated ID intended to aid in discovery of potential security vulnerabilities. The actual impact and attack plausibility have not yet been proven. This ID is fixed in Linux Kernel version v4.19.271 by commit ff85a1dbd90d29f73033177ff8d8de4a27d9721c. For more details please see the references link.