irc: fix memory leak in IRC message parser

Bug was introduced in WeeChat 3.4 by commit
c4b4d80936.

ChangeLog.adoc

@@ -13,7 +13,10 @@ For a list of important changes that require manual actions, please look at rele
 [[v4.0.3]]
 == Version 4.0.3 (under dev)
 
+Bug fixes::
+
   * irc: fix display of self CTCP message containing bold attribute (issue #1981)
+  * irc: fix memory leak in IRC message parser
 
 [[v4.0.2]]
 == Version 4.0.2 (2023-07-12)

src/plugins/irc/irc-message.c

@@ -529,6 +529,8 @@ irc_message_parse_to_hashtable (struct t_irc_server *server,
         free (arguments);
     if (text)
         free (text);
+    if (params)
+        weechat_string_free_split (params);
 
     return hashtable;
 }