[bug] conflict with peekaboo

```vim
" $ uname -r
" 5.13.10-arch1-1
" $ has nvim
" ✓ nvim 0.5.0
" $ has python
" ✓ python 3.9.6
" $ cat test.vim
set runtimepath=$VIMRUNTIME
set runtimepath+=~/.local/share/nvim/repos/github.com/mhinz/vim-startify
set runtimepath+=~/.local/share/nvim/repos/github.com/junegunn/vim-peekaboo
" $ vi -u test.vim
```


Press `"`

Press ``

In the right of window, there exists a new window.

However, if `vi -u test.vim a`, the window will not exist.

Reproduce the behavior with the provided test.vim configuration, Vim/Neovim versions, and the vim-startify and vim-peekaboo runtime paths. Compare `vi -u test.vim` with `vi -u test.vim a`, then trace the plugin startup and quote-handling behavior; done means the extra window no longer appears unexpectedly.

Written by the indexing model from the issue text.