Possible for plot spectrum dialog to not detect spectra

[DanielMurphy22]

Describe the bug Possible to create a workspace where the spectrum number and workspace indicies list are out of sync. Bit of an odd way to create, but I am more worried there's a bug in our plot spectrum dialog than Save/LoadAscii.

To Reproduce

• Download TrainingCourseData from Downloads page
• Open Workbench and load SANSLOQcan2D.nxs
• Run SaveAscii with WriteSpectrumAxisValue set to True (default would be False). You can see my full input below if you need more info.

• Load the saved workspace
• double-click on the workspace to get the plot dialog. The valid Workspace indicies are 0-99, but the valid Spectrum Numbers should be 1-100, not 0.

Platform/Version (please complete the following information): Reproduced on Ubuntu 18.04 and Windows

• Mantid Version: 6.4.20220912

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