SignedCapsulePkg/SystemCapsuleLib: Add ASSERT check for PCD

Add ASSERT check for PCD to avoid platform mis-configuration.

Cc: Chao Zhang <chao.b.zhang@intel.com>
Cc: Qin Long <qin.long@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Jiewen Yao <jiewen.yao@intel.com>
Reviewed-by: Qin Long <qin.long@intel.com>

SignedCapsulePkg/Library/EdkiiSystemCapsuleLib/EdkiiSystemCapsuleLib.c

@@ -415,6 +415,8 @@ ExtractAuthenticatedImage (
   } else {
     return FALSE;
   }
+  ASSERT (PublicKeyData != NULL);
+  ASSERT (PublicKeyDataLength != 0);
 
   Status = AuthenticateFmpImage(
              ImageAuth,