fix: Don't prevent rendering if buffer is empty

[mrjones2014]

I think this: sudo-tee/opencode.nvim#200

Is actually a bug with this plugin.

If the text is non-empty, then is changed to empty via vim.api.nvim_buf_set_lines(buf, 0, -1, false, {}), render-markdown.nvim should still render in that case, otherwise it leaves behind some extmarks (I think those are extmarks)?

[MeanderingProgrammer]

This behavior is intentional and made to support LSP hover docs in older versions of neovim: 059f503

[mrjones2014]

Hm okay interesting. Can you think of a different way to fix this issue?

Basically it leaves codeblock headers around if the buffer is cleared programmatically.