[BUG] cfgparser/stats: fix error message

Fix the error message by unification and goto, previously we had
two independent lists of supported keywords and were raporting 'stats'
instead of a wrong keyword.

Code:
 stats wrong-keyword
 stats

Before:
 [ALERT] 005/163032 (27175) : parsing [haproxy.cfg:248] : unknown stats parameter 'stats' (expects 'hide-version', 'uri', 'realm', 'auth' or 'enable').
 [ALERT] 005/163032 (27175) : parsing [haproxy.cfg:249] : 'stats' expects 'uri', 'realm', 'auth', 'scope' or 'enable', 'hide-version', 'show-node', 'show-desc', 'show-legends'.

After:
 [ALERT] 005/162841 (22710) : parsing [haproxy.cfg:248]: unknown stats parameter 'wrong-keyword', expects 'uri', 'realm', 'auth', 'scope', 'enable', 'hide-version', 'show-node', 'show-desc' or 'show-legends'.
 [ALERT] 005/162841 (22710) : parsing [haproxy.cfg:249]: missing keyword in 'stats', expects 'uri', 'realm', 'auth', 'scope', 'enable', 'hide-version', 'show-node', 'show-desc' or 'show-legends'.
diff --git a/src/cfgparse.c b/src/cfgparse.c
index c0d6dfe..893e16e 100644
--- a/src/cfgparse.c
+++ b/src/cfgparse.c
@@ -1978,10 +1978,8 @@
 		if (curproxy != &defproxy && curproxy->uri_auth == defproxy.uri_auth)
 			curproxy->uri_auth = NULL; /* we must detach from the default config */
 
-		if (*(args[1]) == 0) {
-			Alert("parsing [%s:%d] : '%s' expects 'uri', 'realm', 'auth', 'scope' or 'enable', 'hide-version', 'show-node', 'show-desc', 'show-legends'.\n", file, linenum, args[0]);
-			err_code |= ERR_ALERT | ERR_FATAL;
-			goto out;
+		if (!*args[1]) {
+			goto stats_error_parsing;
 		} else if (!strcmp(args[1], "uri")) {
 			if (*(args[2]) == 0) {
 				Alert("parsing [%s:%d] : 'uri' needs an URI prefix.\n", file, linenum);
@@ -2110,8 +2108,9 @@
 				free(desc);
 			}
 		} else {
-			Alert("parsing [%s:%d] : unknown stats parameter '%s' (expects 'hide-version', 'uri', 'realm', 'auth' or 'enable').\n",
-			      file, linenum, args[0]);
+stats_error_parsing:
+			Alert("parsing [%s:%d]: %s '%s', expects 'uri', 'realm', 'auth', 'scope', 'enable', 'hide-version', 'show-node', 'show-desc' or 'show-legends'.\n",
+			      file, linenum, *args[1]?"unknown stats parameter":"missing keyword in", args[*args[1]?1:0]);
 			err_code |= ERR_ALERT | ERR_FATAL;
 			goto out;
 		}