MdeModulePkg/CapsuleLib: Add NULL capsule name in record.

MdeModulePkg/CapsuleLib: Add NULL capsule name in record.

According to UEFI spec, capsule report variable should include
a null terminator for capsule name and capsule target, if they are
not present.

The reserved field is zeroed.

Cc: Feng Tian <feng.tian@intel.com>
Cc: Star Zeng <star.zeng@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Jiewen Yao <jiewen.yao@intel.com>
Reviewed-by: Feng Tian <feng.tian@intel.com>
Reviewed-by: Star Zeng <star.zeng@intel.com>