ACPICA: Fix NULL pointer dereference in acpi_ns_custom_package()

In the Linux kernel, the following vulnerability has been resolved: ACPICA: Fix NULL pointer dereference in acpi_ns_custom_package() acpi_ns_custom_package() unconditionally dereferences the first element of the package to read the _BIX version number, without checking for NULL: if ((*Elements)->Common.Type != ACPI_TYPE_INTEGER) When firmware returns a _BIX package whose first element is an unresolvable reference, ACPICA evaluates that entry to NULL. acpi_ns_remove_null_elements() does not strip NULL entries for ACPI_PTYPE_CUSTOM packages (fixed-position format would break if elements were shifted), so acpi_ns_custom_package() sees the NULL and causes a crash. Add a NULL check for the first element (version field) before dereferencing it. The caller then receives AE_AML_OPERAND_TYPE instead of crashing.