patch 8.2.1905: the wininfo list may contain stale entries

Problem:    The wininfo list may contain stale entries.
Solution:   When closing a window remove any other entry where the window
            pointer is NULL.

src/buffer.c

@@ -1005,6 +1005,22 @@ free_buffer_stuff(
     VIM_CLEAR(buf->b_start_fenc);
 }
 
+/*
+ * Free one wininfo_T.
+ */
+    void
+free_wininfo(wininfo_T *wip)
+{
+    if (wip->wi_optset)
+    {
+	clear_winopt(&wip->wi_opt);
+#ifdef FEAT_FOLDING
+	deleteFoldRecurse(&wip->wi_folds);
+#endif
+    }
+    vim_free(wip);
+}
+
 /*
  * Free the b_wininfo list for buffer "buf".
  */
@@ -1017,14 +1033,7 @@ clear_wininfo(buf_T *buf)
     {
 	wip = buf->b_wininfo;
 	buf->b_wininfo = wip->wi_next;
-	if (wip->wi_optset)
-	{
-	    clear_winopt(&wip->wi_opt);
-#ifdef FEAT_FOLDING
-	    deleteFoldRecurse(&wip->wi_folds);
-#endif
-	}
-	vim_free(wip);
+	free_wininfo(wip);
     }
 }
 

src/proto/buffer.pro

@@ -8,6 +8,7 @@ int buf_valid(buf_T *buf);
 void close_buffer(win_T *win, buf_T *buf, int action, int abort_if_last, int ignore_abort);
 void buf_clear_file(buf_T *buf);
 void buf_freeall(buf_T *buf, int flags);
+void free_wininfo(wininfo_T *wip);
 void goto_buffer(exarg_T *eap, int start, int dir, int count);
 void handle_swap_exists(bufref_T *old_curbuf);
 char *do_bufdel(int command, char_u *arg, int addr_count, int start_bnr, int end_bnr, int forceit);

src/version.c

@@ -750,6 +750,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1905,
 /**/
     1904,
 /**/

src/window.c

@@ -5015,7 +5015,26 @@ win_free(
     FOR_ALL_BUFFERS(buf)
 	FOR_ALL_BUF_WININFO(buf, wip)
 	    if (wip->wi_win == wp)
+	    {
+		wininfo_T	*wip2;
+
+		// If there already is an entry with "wi_win" set to NULL it
+		// must be removed, it would never be used.
+		for (wip2 = buf->b_wininfo; wip2 != NULL; wip2 = wip2->wi_next)
+		    if (wip2->wi_win == NULL)
+		    {
+			if (wip2->wi_next != NULL)
+			    wip2->wi_next->wi_prev = wip2->wi_prev;
+			if (wip2->wi_prev == NULL)
+			    buf->b_wininfo = wip2->wi_next;
+			else
+			    wip2->wi_prev->wi_next = wip2->wi_next;
+			free_wininfo(wip2);
+			break;
+		    }
+
 		wip->wi_win = NULL;
+	    }
 
 #ifdef FEAT_SEARCH_EXTRA
     clear_matches(wp);