script/execute: Fix potential underflow and NULL dereference

script/execute: Fix potential underflow and NULL dereference

The result is initialized to 0 in grub_script_arglist_to_argv().
If the for loop condition is not met both result.args and result.argc
remain 0 causing result.argc - 1 to underflow and/or result.args NULL
dereference. Fix the issues by adding relevant checks.

Fixes: CID 473880
Signed-off-by: Lidong Chen <lidong.chen@oracle.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
Gbp-Pq: Topic cve-2025-jan
Gbp-Pq: Name script-execute-Fix-potential-underflow-and-NULL-dereferen.patch