Not Finding Rels File

[oleibman]

Fix #3553. Read of /xl/worksheets/_rels/sheet1.xml.rels fails on the new test worksheet (generated by 3rd party product), but read of xl/worksheets/_rels/sheet1.xml.rels (same name without leading slash) succeeds. Problem is that 3rd party product generates references with unexpected leading slash.

This is:

• a bugfix
• a new feature
• refactoring
• additional unit tests

Checklist:

• Changes are covered by unit tests
  • Changes are covered by existing unit tests
  • New unit tests have been added
• Code style is respected
• Commit message explains why the change is made (see https://github.com/erlang/otp/wiki/Writing-good-commit-messages)
• CHANGELOG.md contains a short summary of the change and a link to the pull request if applicable
• Documentation is updated as necessary

Why this change is needed?

Provide an explanation of why this change is needed, with links to any Issues (if appropriate).
If this is a bugfix or a new feature, and there are no existing Issues, then please also create an issue that will make it easier to track progress with this PR.

[oleibman]

The problem in the original file is in _rels/.rels:

<?xml version="1.0" encoding="utf-8"?>
<Relationships xmlns="http://schemas.openxmlformats.org/package/2006/relationships">
<Relationship Type="http://schemas.openxmlformats.org/officeDocument/2006/relationships/officeDocument" Target="/xl/workbook.xml" Id="rId2" />
<Relationship Type="http://schemas.openxmlformats.org/package/2006/relationships/meatadata/core-properties" Target="/docProps/core.xml" Id="rId4" />
<Relationship Type="http://schemas.openxmlformats.org/officeDocument/2006/relationships/extended-properties" Target="/docProps/app.xml" Id="rId5" />
</Relationships>

The Target attributes all have leading slashes. In most (virtually all) Excel files, there is no leading slash. This suggests that the solution belongs where _rels/.rels is read. I will make that change. Unfortunately, for the file in question, there is nothing in core properties, and extended properties does not include any properties captured by PhpSpreadsheet, so the only thing we can test from this file remains the hyperlink.