Tiff Viewer shows wrong page after switching color map

[kostrykin]

Describe the bug
When the Tiff Viewer is used for visualization of a multi-page Tiff (e.g., a z-stack) and the color map is switched, the Viewer wrongly shows the first page instead of the previously selected page. One has to manually update the currently selected page to ensure that the correct page is shown again.

Galaxy Version and/or server at which you observed the bug
Galaxy Version: {"version_major":"26.0","version_minor":"1.dev0"} (usegalaxy.eu)

Browser and Operating System
Operating System: macOS
Browser: Firefox

To Reproduce
Steps to reproduce the behavior:

1. Open any multi-page Tiff inside the Tiff Viewer
2. Change the page to any page but Page 1
3. Change the color map
4. Observe that the page displayed now is Page 1

Expected behavior
The page displayed should remain the same.

Screenshots

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