State what is the current stop condition in iso639_lang_t.

src/text/iso-639_def.h

@@ -201,6 +201,8 @@ static const iso639_lang_t p_languages[] =
     { N_( "Yoruba" ),           "",            "yo", "yor", "yor" },
     { N_( "Zhuang" ),           "",            "za", "zha", "zha" },
     { N_( "Zulu" ),             "",            "zu", "zul", "zul" },
+
+    /* XXX psz_eng_name MUST be NULL on the last item as it is the stop condition */
     { NULL,                   NULL,            "",   "",    "" }
 };