Fix the bug in F1AdaptiveThreshold which occurs only when there are no anomalous images in a validation set

[tanemaki]

📝 Description

• Fix the bug in F1AdaptiveThreshold which occurs only when there are no anomalous images in a validation set
• 🛠️ Fixes [Bug]: F1AdaptiveThreshold incorrectly selects minimum value when no anomalous images are in validation set #2433

✨ Changes

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• 🐞 Bug fix (non-breaking change which fixes an issue)
• 🔨 Refactor (non-breaking change which refactors the code base)
• 🚀 New feature (non-breaking change which adds functionality)
• 💥 Breaking change (fix or feature that would cause existing functionality to not work as expected)
• 📚 Documentation update
• 🔒 Security update

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[djdameln]

Thanks for your PR. This is a useful addition. Previously the metric would implicitly return the maximum value when all images were normal, but as it shows this was not a robust approach. Explicitly checking these edge cases is much better. I do have 2 suggestions for improvement, see below.