Append the terminating null character at the end of the string to avoid buffer overflow.

Append the terminating null character at the end of the string to avoid buffer overflow.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Qiu Shumin <shumin.qiu@intel.com>
Reviewed-by: Fu Siyuan <siyuan.fu@intel.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@15888 6f19259b-4bc3-4df7-8a09-765794883524