Cannot save empty file because ensure_final_newline_on_save adds a newline

[injust]

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Describe the bug / provide steps to reproduce it

With ensure_final_newline_on_save enabled (which is by default), Zed adds a newline to empty files, making it impossible to save an actually empty file.

This is technically correct, as an empty file doesn't have a trailing newline...but you probably never want this behaviour.

Zed Version and System Specs

Zed: v0.166.1 (Zed)
OS: macOS 15.2.0
Memory: 16 GiB
Architecture: x86_64

If applicable, add screenshots or screencasts of the incorrect state / behavior

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If applicable, attach your Zed.log file to this issue.

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[SomeoneToIgnore]

Duplicate of #11044