Fix bug in plotting Qspace integration in BaseSX class

Fix bug in plotting Qspace integration in BaseSX class when no signal (i.e. data all 0s) Updated a test to stop regression and noticed that original test was failing on main locally - I think there was a typo in CmakeLists that meant unit tests for BaseSX weren't running - hopefully this fixes it!

Fixes #37506

Report to: Nick Funnell

To test:

(1) Run this without error

from mantid.simpleapi import *
from Diffraction.single_crystal.base_sx import BaseSX

# create  peeak table
ws = LoadEmptyInstrument(Filename="SXD_Definition.xml", OutputWorkspace="empty")
axis = ws.getAxis(0)
axis.setUnit("TOF")
peaks = CreatePeaksWorkspace(InstrumentWOrkspace=ws, NumberOfPeaks=0)
AddPeak(PeaksWorkspace=peaks, RunWorkspace=ws, TOF=1000, DetectorID=35004)

# make empty MD workspace
md = CreateMDWorkspace(Dimensions=3, Extents=[0,1,0,1,0,1], Names="Qx,Qy,Qz", 
                       Frames='QLab,QLab,QLab',Units='Ang^-1,Ang^-1,Ang^-1')
# integrate
peaks_int = IntegratePeaksMD(InputWorkspace=md, PeakRadius=0.1, BackgroundInnerRadius=0.12, 
                            BackgroundOuterRadius=0.13, PeaksWorkspace=peaks)
# plot
BaseSX.plot_integrated_peaks_MD(md, peaks_int, r"\\olympic\Babylon5\Public\RWaite\test_plot_MD.pdf", nbins_max=21, extent=1.5, log_norm=True)

This does not require release notes because was added this release

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mantidproject / mantid