CVE-2025-38208 smb: client: add NULL check in automount_fullpath

In the Linux kernel, the following vulnerability has been resolved: smb: client: add NULL check in automountfullpath page is checked for null in buildpathfromdentryoptionalprefix when tcon-originfullpath is not set. However, the check is missing when it is set. Add a check to prevent a potential...