patch 8.2.3572: memory leak when closing window and using "multispace"

Problem:    Memory leak when closing window and using "multispace" in
            'listchars'.
Solution:   Free the memory. (closes #9071)
diff --git a/src/window.c b/src/window.c
index b0bdd59..5de6ed7 100644
--- a/src/window.c
+++ b/src/window.c
@@ -5041,6 +5041,8 @@
     clear_winopt(&wp->w_onebuf_opt);
     clear_winopt(&wp->w_allbuf_opt);
 
+    vim_free(wp->w_lcs_chars.multispace);
+
 #ifdef FEAT_EVAL
     vars_clear(&wp->w_vars->dv_hashtab);	// free all w: variables
     hash_init(&wp->w_vars->dv_hashtab);