buflist: fix memory leak when reading config and changing option buflist.look.sort

ChangeLog.adoc

@@ -21,6 +21,7 @@ https://weechat.org/files/releasenotes/ReleaseNotes-devel.html[release notes]
 Bug fixes::
 
   * core: fix bad window size on startup with some terminals like https://github.com/kovidgoyal/kitty[kitty] (issue #1769)
+  * buflist: fix memory leak when reading config and changing option buflist.look.sort
   * relay: fix save of channels in autojoin option when JOIN and PART commands are received from an IRC relay client (issue #1771)
 
 [[v3.5]]

src/plugins/buflist/buflist-config.c

@@ -323,6 +323,8 @@ buflist_config_change_sort (const void *pointer, void *data,
             free (sort);
     }
 
+    weechat_hashtable_free (hashtable_pointers);
+
     buflist_bar_item_update (0);
 }