Exact match in VLOOKUP now returns first match

[frantzmiccoli]

This is:

- [x] a bugfix
- [ ] a new feature

Checklist:

• Changes are covered by unit tests
• 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

Why this change is needed?

I stumbled upon a case where the value of a VLOOKUP was incorrectly returned compared with Excel.

I have also observed that PHP associative sorting does not preserve key order (for keys which have the same value), which explain the extra test on line 729. See https://gist.github.com/frantzmiccoli/bd03395b8fc831c67828718192c214b8 if you wish to test for yourself with asort. uasort behaves the same way but the gist was quicker to write with asort.

[PowerKiKi]

Thanks ! I merged with a few modifications