Werk #944: oracle_tablespaces: fixed calculation of space left and number of remaining increments

The remaining increments and space left was not correctly calculated when the remaining memory space was not a multiple of the increment size.
For example:

Tablespace
900 MB used
100 MB free space for autoincrement

200 MB increment size

The previous version calculated 900 MB as maximum size, because the increment size was greater than the remaining autoincrement space. This was wrong. The last increment also uses the remaining space, even if the remaining size is smaller than the increment size.

As a result, this fix actually increases the amount of available free space, so it should not have any negative side effects for already configured limits.

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