Text gets deleted if command fails

[asmeurer]

If you run a command like ellama-improve-grammar on a selection, but the command fails for some reason, the paragraph is just completely deleted. For example, this happened to me because I misconfigured my OpenAI API key permissions, but I imagine it could also happen if the API service or my internet went down.

I think it would be better if ellama commands like this did not actually attempt to delete any text from the buffer until the LLM command completes. Perhaps there's an issue with race conditions here, but I would even be OK if it blocked (so long as there was some sort of progress indicator).

At the very least, though, if a command fails for some reason, it should reinsert the original text into the buffer.

[s-kostyaev]

Blocker for this issue ahyatt/llm#37