Drowning in Warning Messages with Corrupt Xls File

[oleibman]

Fix #4647. Xls file is corrupt - PhpSpreadsheet tries to extract a substring using array notation, but the index is out of bounds. Php treats this as a warning situation, so continues to process, leading to an onslaught of warning messages. We could change to use the substr function rather than array notation, but that seems inappropriate - it would be better to throw an exception and have the user fix the file. In the file posted with the issue, opening it with Excel, and responding yes when it asks if it's okay to clean up the corruption, yields a usable file. Unfortunately, that file weighs in at 28MB, much too large for our test suite. So, no new unit tests accompany this change, but it has been tested.

Tests are added to getUint2d, which seems to be the source of the problem in the sample file, and, for good measure, getInt2d and getInt4d. There may be other sources of similar corruption, but we'll stick with what's in front of our nose.

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