Don't return too early, clean vars first (l10ntools/treemerge)

Change-Id: Ib99e0897fa36bdd0c8d805e38e77c3d626c0569a
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/96302
Tested-by: Jenkins
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>

l10ntools/source/treemerge.cxx

@@ -131,7 +131,7 @@ namespace
                 std::cerr
                     << "Treex error: Cannot find title in "
                     << sXhpPath << std::endl;
-                return nullptr;
+                pReturn = nullptr;
             }
             xmlFreeDoc( pXhpFile );
             xmlCleanupParser();