Fix two issues:

1. EDK II StrnCpy does not necessarily "0" terminate destination string if the source string length is larger than "n". Caller needs to terminate it itself.
2. The definition of EFI_HII_CALLBACK_PACKET has been changed to follow framework HII spec 0.92, we need to change the corresponding code correctly.

git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@4270 6f19259b-4bc3-4df7-8a09-765794883524

IntelFrameworkModulePkg/Universal/SetupBrowserDxe/Presentation.c

@@ -1236,7 +1236,7 @@ Returns:
       Selection->ThisTag->StorageWidth
       );
 
-    if (Packet != NULL) {
+    if (Packet != NULL && Packet->String != NULL) {
       //
       // Upon error, we will likely receive a string to print out
       //