The new version contains some improvements in handling mocks (sebastianbergmann/phpunit#3602) and will help identify some existing issues in DBAL 3.0 tests:

There were 2 warnings:

1) Doctrine\Tests\DBAL\Driver\OCI8\OCI8StatementTest::testExecute with data set #0 (array('test', null, 'value'))
Method bindValue may not return value of type boolean

2) Doctrine\Tests\DBAL\Driver\OCI8\OCI8StatementTest::testExecute with data set #1 (array(null, 'test', 'value'))
Method bindValue may not return value of type boolean

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|      Q       |   A
|------------- | -----------
| Type         | bug
| Fixed issues | doctrine#6038

#### Summary

As described in the mentioned issue, `-0.5` from `-1 / 2` will raise
type error when trying to `setLength`

```
Argument #1 ($length) must be of type ?int, float given
```

https://github.com/doctrine/dbal/blob/8bc0d9ae42f20af54120396ef7a1b3248479c2b5/src/Schema/Column.php#L78

This PR check if length is `-1` and keep it as is before perform
division.