irc: sent "QUIT" message to servers connected with TLS on /upgrade

ChangeLog.adoc

@@ -24,6 +24,7 @@ Bug fixes::
   * core: force key "return" to command "/input return" when migrating legacy keys
   * core: display actual key name and command with key kbd:[Alt+k], remove key kbd:[Alt+K] (grab raw key) and associated commands `/input grab_raw_key` and `/input grab_raw_key_command`
   * irc: reply to a CTCP request sent to self nick (issue #1966)
+  * irc: sent "QUIT" message to servers connected with TLS on `/upgrade`
 
 [[v4.0.0]]
 == Version 4.0.0 (2023-06-24)

src/plugins/irc/irc.c

@@ -149,6 +149,8 @@ irc_signal_upgrade_cb (const void *pointer, void *data,
                       "work for servers connected via TLS"),
                     weechat_prefix ("error"), IRC_PLUGIN_NAME);
             }
+            /* send QUIT to server, then disconnect */
+            irc_command_quit_server (ptr_server, NULL);
             irc_server_disconnect (ptr_server, 0, 0);
             /*
              * schedule reconnection: WeeChat will reconnect to this server