NULL pointer deference in acpi_db_convert_to_package of Linux acpi module

The memory allocation function ACPI_ALLOCATE_ZEROED does not guarantee a

successful allocation, but the subsequent code directly dereferences the

pointer that receives it, which may lead to null pointer dereference.

To fix this issue, a null pointer check should be added. If it is null,

return exception code AE_NO_MEMORY.