Ubuntu: (Multiple Advisories) (CVE-2025-38077): Linux kernel vulnerabilities

In the Linux kernel, the following vulnerability has been resolved:

platform/x86: dell-wmi-sysman: Avoid buffer overflow in current_password_store()

If the 'buf' array received from the user contains an empty string, the
'length' variable will be zero. Accessing the 'buf' array element with
index 'length - 1' will result in a buffer overflow.

Add a check for an empty string.

Found by Linux Verification Center (linuxtesting.org) with SVACE.