Update Xlsx.php

[riverdale74]

Handle "default" cases by creating an empty string table entry.

I added these lines after observing that $sharedStrings was being indexed incorrectly with a test xlsx file. Adding these lines fixes that error.

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.

Handle "default" cases by creating an empty string table entry.

I added these lines after observing that $sharedStrings was being indexed incorrectly with a test xlsx file. Adding these lines fixes that error.

[oleibman]

Can you provide a unit test that will demonstrate the issue, and prove that this fix works?

[oleibman]

No update in over a year. Closing.