MdeModulePkg/HiiDatabaseDxe: ASSERT StringPtr

The caller of CompareAndMergeDefaultString has checked that
AltCfgResp must contain AltConfigHdr. So we add ASSERT to assume
StringPtr is not NULL.

Cc: Dandan Bi <dandan.bi@intel.com>
Cc: Eric Dong <eric.dong@intel.com>
Signed-off-by: Shenglei Zhang <shenglei.zhang@intel.com>
Reviewed-by: Dandan Bi <dandan.bi@intel.com>

MdeModulePkg/Universal/HiiDatabaseDxe/ConfigRouting.c

@@ -909,6 +909,7 @@ CompareAndMergeDefaultString (
   // To find the <AltResp> with AltConfigHdr in AltCfgResp, ignore other <AltResp> which follow it.
   //
   StringPtr = StrStr (*AltCfgResp, AltConfigHdr);
+  ASSERT (StringPtr != NULL);
   StringPtrNext = StrStr (StringPtr + 1, L"&GUID");
   if (StringPtrNext != NULL) {
     TempCharA = *StringPtrNext;