cli: Make zed --wait --diff not wait until window close

[timvermeulen]

zed --wait --diff <left> <right> currently waits for the entire window to close instead of just the diff itself, due to the combination of

• zed --diff adds the cwd to the paths to open (see cli: Teach --diff to recurse into directories and add a MultiDiffView #45131), and
• passing a directory to zed --wait blocks until the Zed window is closed (see Make zed --wait work with directories #44936), which doesn't distinguish between explicit paths and the one zed --diff adds

Fixed by only running the zed --wait <dir> logic to block until the window is closed in case the user actually passed any non-diff paths.

I've confirmed locally that it works, though I wasn't really sure how to write a good test for this.

Self-Review Checklist:

• I've reviewed my own diff for quality, security, and reliability
• Unsafe blocks (if any) have justifying comments
• The content is consistent with the UI/UX checklist
• Tests cover the new/changed behavior
• Performance impact has been considered and is acceptable

Release Notes:

• zed --wait --diff <left> <right> now blocks until the diff is closed, and not until the entire window is closed.

[ChristopherBiscardi]

Thanks :) I've verified that this works as expected