Update detect.py (Fix save-csv: Ensure header is written to CSV)

[aligh993]

This commit resolves an issue where the save-csv command did not write the CSV header. The code now correctly saves the header in the CSV file.

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🛠️ PR Summary

_{Made with ❤️ by Ultralytics Actions}

🌟 Summary

Enhanced CSV logging functionality in YOLOv5 for improved usability and bug prevention. 🛠️📊

📊 Key Changes

• Fixed a bug in detect.py where CSV headers were inconsistently written.
• Replaced the incorrect csv_path.is_file() check with os.path.isfile(csv_path) for proper file validation before appending data.

🎯 Purpose & Impact

• 🐛 Bug Fix: Ensures headers in the CSV file are only written once, preventing duplicates or formatting issues.
• 📂 Improved Usability: Guarantees smooth operation of prediction logging, especially during repeated runs.
• 📈 User Benefit: Users analyzing predictions through CSV logs now experience more reliable and clean data formatting.

[github-actions]

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[UltralyticsAssistant]

🚀 Big news! The PR by @aligh993 with contributions from @glenn-jocher has officially been merged. 🎉 Your dedication and attention to detail have elevated YOLOv5’s CSV logging to new heights—helping ensure clean, reliable, and user-friendly data handling for all. 📊✨

As Marcus Aurelius once said, "What we do now echoes in eternity." Your fixes might feel like small steps, but they create ripples of impact for researchers, developers, and innovators worldwide. 🌍 Thank you both for making a difference—one line of code at a time! ❤️🙏