Warning that applying a template will replace the existing issue description should only show up when the user already has written content into the issue description

Summary

When I'm opening a new issue, I always select a template first before writing any content. When I do so, it shows me a message that applying this template will replace the issue description.

Because I haven't written anything into the issue description yet, having to click on "Apply template" is both unnecessary and annoying to me.

/cc @hollyreynolds @pedroms As this shows up both for new issues as well as for new merge requests, I'm not sure which group it should fall into. I picked groupproject management because I expect more issues to be created than merge requests, and it would thus have more impact on that part, but feel free to change that 🙂