Handle corner cases of interactively entered commit messages — heartwood

Split on double newline fails when description is empty
Title must be a single line

         placeholder.push_str(help);
         let output = Self::Edit.get(&placeholder)?;
         let Some((title, description)) = output.split_once("\n\n") else {
             return Ok(None);
         let output = match output.split_once("\n\n") {
             Some((x, y)) => Some((x, y)),
             None => Some((output.as_str(), "")),
         };
         let Some((title, description)) = output else {
             return Ok(None)
         };
         let (title, description) = (title.trim(), description.trim());
         if title.is_empty() {
         if title.is_empty() | title.contains('\n') {
             return Ok(None);
         }
         Ok(Some((title.to_owned(), description.to_owned())))