Fix check_suffix()

[glenn-jocher]

Fix a bug in #4711 when file=''

🛠️ PR Summary

_{Made with ❤️ by Ultralytics Actions}

🌟 Summary

Improved file suffix checking in utility functions.

📊 Key Changes

• Modified check_suffix logic to require a non-empty file parameter.
• Made check_suffix call in check_file optional.

🎯 Purpose & Impact

• These changes ensure that file checks only proceed if a file name is provided, preventing unnecessary checks on empty strings or None.
• The update will result in cleaner code and potentially avoid errors where incorrect file paths might have been accepted.
• Users should experience more robust file handling, especially when dealing with model weights and configuration files. 🛠️📁