xmlhelp: Add missing include

Change-Id: Ie369f00a745dba82c8966f51886d74a8a9a7c1ff
Reviewed-on: https://gerrit.libreoffice.org/18523Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: David Ostrovsky <david@ostrovsky.org>

xmlhelp/source/cxxhelp/provider/resultsetforquery.cxx

@@ -17,6 +17,8 @@
  *   the License at http://www.apache.org/licenses/LICENSE-2.0 .
  */
 
+#include <iterator>
+
 #include <comphelper/processfactory.hxx>
 #include <com/sun/star/ucb/Command.hpp>
 #include <com/sun/star/ucb/XCommandEnvironment.hpp>