Fix pivot subtotals loading

[b0bi79]

ClosedXML does not correctly define the properties of subtotals for records, like this:

<pivotField showAll="0">
...
<dataField name="Sum Amount paid" fld="6" subtotal="sum" baseField="0" baseItem="0"/>

In this case, Excel shows subtotals, but after loading into ClosedXML and then saving the document, the subtotals are turned off.

[b0bi79]

This PR is needed for the release of ClosedXML.Report

[igitur]

Do you have a unit test for this?

[igitur]

I also notice that if I apply these commits on top of #1196 's branch, then it breaks #1196 's unit tests. The generated pivot table in TwoPivotWithOneSourceTest changes from not having subtotals to having subtotals. Not sure whether this intended.

[b0bi79]

Today I can't, but tomorrow I will check and add new tests.

[igitur]

Please rebase this on develop. With #1196 now merged, I think that you will now already have a test case for this.

[igitur]

You should have rebased, not merged.

[b0bi79]

I tried to rebase, but apparently did something wrong. How can I cancel this?

[igitur]

I'll do it and push to your branch a bit later. I don't want you to accidentally delete the work you've done.

[b0bi79]

Sorry, I don't work well with git. Thank you.

[igitur]

This is how I rebased on develop.

[igitur]

Do a git pull origin/fix_pivot_subtotals_loading --rebase on your side.

[igitur]

Please unhide all sheets in the reference files. Hidden sheets add to confusion ;-)

[igitur]

Also try to simplify Sheet1 in order to keep the file as small as possible. For example, we don't need the image in the first row.

[igitur]

I rewrote the commit history and pushed to your branch. If the CI tests pass, I will merge.

[igitur]

Thanks for the contribution. We're making good progress now.