add condition judgment to avoid accessing NULL address if not found existing variable.

git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@9038 6f19259b-4bc3-4df7-8a09-765794883524

MdeModulePkg/Universal/Variable/EmuRuntimeDxe/EmuVariable.c

@@ -767,7 +767,9 @@ UpdateVariable (
   //
   // Mark the old variable as deleted
   //
+  if (Variable->CurrPtr != NULL) {
     Variable->CurrPtr->State &= VAR_DELETED;
+  }
 
   UpdateVariableInfo (VariableName, VendorGuid, Variable->Volatile, FALSE, TRUE, FALSE, FALSE);