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 v4.14.304 by commit dd83a9763e29ed7a21c8a43f7a62cd0a6bf74692. For more details please see the references link.