UPT used to use "B:" as the temp directory which may cause conflict,
now it will choose a valid volume. Also UPT now accepts empty sections.
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Hess Chen <hesheng.chen@intel.com>
Reviewed-by: Yonghong Zhu <yonghong.zhu@intel.com>