Libde265 `Slice index` not working

[th1nk3r-ing]

Describe the bug
Libde265 Slice index not working in the latest source ([feature/RGB565](https://github.com/IENT/YUView/tree/refs/heads/feature/RGB565))

To Reproduce
Steps to reproduce the behavior:

1. Go to '...'
2. Click on '....'
3. Scroll down to '....'
4. See error

Expected behavior
A clear and concise description of what you expected to happen.

Screenshots
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Version (please complete the following information):

• OS: [e.g. iOS]
• Version [e.g. 2.2.1, commit gb283bgrj]
• If you compiled YUView yourself then which Qt version did you use?