Fixed thickness calculation for sensitive surface

[henryg7vdj]

Briefly, what does this PR introduce?

I believe there is a minor bug in the calculation of the inner and outer thicknesses for the sensitive surface in BarrelTrackerWithFrame_geo.cpp. When there are two sensitive compositions placed at the same z position, the thicknesses for the second are incorrect because of the order in which the calculation is done.

To fix this, I moved the thickness_so_far calculation to before the if (x_comp.isSensitive()) { section, and changed the sign of + x_comp.thickness() / 2.0 when it is used to calculate the inner and outer thicknesses.

Before the fix:

	sensor	thickness_so_far	inner_thickness		outer_thickness
L3	1		0.213875			0.219275 			0.0054
	2		0.224675			0.230075 			-0.0054
L4	1		0.218605			0.224005			0.0054
	2		0.229405			0.234805 			-0.0054

After the fix:

L3	1		0.224675			0.219275 			0.0054
	2		0.224675			0.219275 			0.0054
L4	1		0.229405			0.224005 			0.0054
	2		0.229405			0.224005 			0.0054

I hope this has fixed the issue.

What kind of change does this PR introduce?

• [x ] Bug fix (issue #__)
• New feature (issue #__)
• Documentation update
• Other: __

Please check if this PR fulfills the following:

• Tests for the changes have been added
• Documentation has been added / updated
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Does this PR introduce breaking changes? What changes might users need to make to their code?

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