fixed doublicate key issue
Merge pull request #1566 from drummer3333/1.3

This PR was merged into zikula:1.3 branch.

Discussion
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fixed doublicate key issue with categories

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | https://github.com/Guite/MostGenerator/issues/472
| Refs tickets  | -
| License       | MIT
| Doc PR        | -

PR #1561 added the problem, that the category entities cannot deleted an added in the same flush process.
This PR deletes only nonselected from and adds only new categorys to the entity.

Commits
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e44b73ac39650e13ac2850d9022de904b5b5208c fixed doublicate key issue drummer3333