Body override lost if result is invalid

[LucasPickering]

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Describe the bug
A clear and concise description of what the bug is

If you override a raw/JSON body in the TUI but the provided template is invalid, the body reverts to the default from the recipe. This can be frustrating if you made a bunch of changes that are now lost.

To Reproduce
Steps to reproduce the behavior

1. Create a recipe with a raw body
2. Open it in the TUI
3. Edit the body
4. Change it to make it an invalid template (e.g. have an opening {{ with no closing }})
5. Save and exit
6. When returning to the TUI, it will show the parse error but the body override will be the default from the recipe

Expected behavior
A clear and concise description of what you expected to happen

The editor should retain the invalid body but make it clear in the UI that it's not valid. The invalid body should not block sending a request. When a request is sent, we have two options:

• Use the default from the recipe
• Use the invalid body
  The first option is easier, especially for JSON bodies, because plumbing around an invalid template/JSON object is a lot harder. Whatever we choose, it should be clear to the user what will happen.

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Additional context
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