Fix division by zero warning

[zakariaejaidi]

PHP Warning: Division by zero in /vendor/phpoffice/phpspreadsheet/src/PhpSpreadsheet/Calculation/Financial/CashFlow/Variable/Periodic.php on line 155

This is:

- [ x] 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
• [x] 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
• [ ] Documentation is updated as necessary

[MarkBaker]

When we implement a bugfix, we always try to create a unit test to verify the original problem and confirm that the bugfix works as expected. Would you be able to create a unit test for this fix?

[oleibman]

No update in over a year. Closing.