Sliceviewer: Log colourbar scale option not disabled outside data.

[cailafinn]

Describe the bug Manual testing instructions say

"Zoom in to a region outside the extent of the data, check the Log colorscale option is disabled."

This does not occur.

To Reproduce https://developer.mantidproject.org/Testing/SliceViewer/SliceViewer.html

1. Load some data
2. Open the sliceviewer
3. Move the view outside the data
4. Switch to log
5. This should not be possible.

Expected behavior Either log scaling should be disabled or the manual testing instructions should be updated.

Platform/Version (please complete the following information):

• OS: macOS
• OS Version: 14 Sonoma
• Mantid Version 6.8