patch 8.2.4631: crash when switching window in BufWipeout autocommand

Problem:    Crash when switching window in BufWipeout autocommand.
Solution:   Put any buffer in the window to avoid it being NULL.
            (closes #10024)
diff --git a/src/testdir/test_autocmd.vim b/src/testdir/test_autocmd.vim
index 688508a..39ba9af 100644
--- a/src/testdir/test_autocmd.vim
+++ b/src/testdir/test_autocmd.vim
Binary files differ