fix(buffer): disable buffer-updates before removing from window #18933

There can be other places that access window buffer info (e.g.
`tabpagebuflist()`), so checking `w_closing` in `win_findbuf()` doesn't
solve the crash in all cases, and may also cause Nvim's behavior to
diverge from Vim.

Fix #14998

src/nvim/window.c

@@ -7297,7 +7297,7 @@ void win_findbuf(typval_T *argvars, list_T *list)
   int bufnr = tv_get_number(&argvars[0]);
 
   FOR_ALL_TAB_WINDOWS(tp, wp) {
-    if (!wp->w_closing && wp->w_buffer->b_fnum == bufnr) {
+    if (wp->w_buffer->b_fnum == bufnr) {
       tv_list_append_number(list, wp->handle);
     }
   }