parse pivotTable faild due to a nil pointer

[leko-W]

Description

代码在xmlPivotCache.go文件中存在xlsxCacheSource结构体，内部有5个标签：type、connectionId、worksheetSource、consolidation、extLst

源文件打开成xml后，cacheSource 标签如下：， 不存在worksheetSource标签，WorksheetSource属性本身为空，导致后面代码取出pc.CacheSource.WorksheetSource.Sheet时出现空指针

Steps to reproduce the issue

1. 本地文件xml如下

<pivotCacheDefinition xmlns="http://schemas.openxmlformats.org/spreadsheetml/2006/main" xmlns:r="http://schemas.openxmlformats.org/officeDocument/2006/relationships" xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" xmlns:xr="http://schemas.microsoft.com/office/spreadsheetml/2014/revision" mc:Ignorable="xr" saveData="0" refreshedBy="AAAA" refreshedDate="45827.477583680557" backgroundQuery="1" createdVersion="7" refreshedVersion="7" minRefreshableVersion="3" recordCount="0" supportSubquery="1" supportAdvancedDrill="1" xr:uid="{C3EDE0DE-36B2-4F3A-856D-0066D92D664C}">
<cacheSource type="external" connectionId="1"/>
中间内容不方便透露
</pivotCacheDefinition>

Describe the results you received

"msg":"runtime error: invalid memory address or nil pointer dereference"

.../github.com/xuri/excelize/v2.(*File).getPivotTable
.../github.com/xuri/excelize/v2@v2.9.1-0.20250105013731-af422e17009b/pivotTable.go:875
.../github.com/xuri/excelize/v2.(*File).GetPivotTables
.../github.com/xuri/excelize/v2@v2.9.1-0.20250105013731-af422e17009b/pivotTable.go:803

Describe the results you expected

success

Go version

1.22

Excelize version or commit ID

github.com/xuri/excelize/v2 v2.9.1-0.20250105013731-af422e17009b

Environment

Microsoft Excel

Validations

• Check that there isn't already an issue that reports the same bug to avoid creating a duplicate.
• The provided reproduction is a minimal reproducible example of the bug.

[xuri]

Thanks for your issue. This issue has been fixed, please upgrade to the master branch code by go get -u github.com/xuri/excelize/v2@master, and this patch will be released in the next version.