Refine code to make it more safely.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Eric Dong <eric.dong@intel.com>
Reviewed-by: Feng Tian <feng.tian@intel.com>

git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@15598 6f19259b-4bc3-4df7-8a09-765794883524

MdeModulePkg/Universal/Network/IScsiDxe/IScsiMisc.c

@@ -219,6 +219,7 @@ IScsiLunToUnicodeStr (
     TempStr += StrLen (TempStr);
   }
 
+  ASSERT (StrLen(Str) >= 1);
   Str[StrLen (Str) - 1] = 0;
 
   for (Index = StrLen (Str) - 1; Index > 1; Index = Index - 2) {