patch 8.2.0636: :messages does not show the maintainer when $LANG is unset

Problem:    :messages does not show the maintainer when $LANG is unset.
Solution:   Call get_mess_lang() if available. (closes #5978)

src/message.c

@@ -1035,7 +1035,11 @@ ex_messages(exarg_T *eap)
 
     if (p == first_msg_hist)
     {
+#ifdef FEAT_MULTI_LANG
+	s = get_mess_lang();
+#else
 	s = mch_getenv((char_u *)"LANG");
+#endif
 	if (s != NULL && *s != NUL)
 	    // The next comment is extracted by xgettext and put in po file for
 	    // translators to read.

src/version.c

@@ -746,6 +746,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    636,
 /**/
     635,
 /**/