ACPICA: Object repair: Allow 0-length packages for variable-length packages

For the predefined names that return fully variable-length
packages, allow a zero-length package with no warning, since it
is technically a legal construct (and BIOS writers use it.)

Signed-off-by: Bob Moore <robert.moore@intel.com>
Signed-off-by: Lv Zheng <lv.zheng@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>