Fix metadata template issue when using Adetailer

[liamkerr]

This PR fixes a bug with how the prompt template is saved when using Adetailer: https://github.com/adieyal/sd-dynamic-prompts/issues/703

I'm not sure why Adetailer does this, but after it processes an image, it calls the process() function of dynamic-prompts a second time and, during this second execution, dynamic-prompts overwrites its template metadata with a prompt value that no longer contains template information.

So this PR just makes sure not to overwrite the template metadata after it's written correctly the first time.

[bluelovers]

https://github.com/adieyal/sd-dynamic-prompts/pull/790