CryptoPkg: Add some comments for API usage clarification.

This patch adds some comments for API usage clarification, and
adds one object initialization in X509ConstructCertificateStack
implementation to fix possible memory release issue.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Qin Long <qin.long@intel.com>
Reviewed-by: Ting Ye <ting.ye@intel.com>

git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@17671 6f19259b-4bc3-4df7-8a09-765794883524
5 files changed