[stable9] Change order of share creation validation

[PVince81]

Makes sure that the share owner is set before entering the checks that
need it.

Partial backport of afa37d3 from

Fixes #25359 which is a regression from OC 8.2.

I will add an integration test for this to avoid future regressions.

[mention-bot]

@PVince81, thanks for your PR! By analyzing the annotation information on this pull request, we identified @rullzer, @LukasReschke and @nickvergessen to be potential reviewers

[PVince81]

Integration test added. I'll forward port it to master.

Please review @owncloud/sharing @DeepDiver1975 @georgehrke @guruz

[SergioBertolinSG]

I'll seeing something that not sure if it correct but doesn't seems to be. After following the steps of #25359 user2 has three folders same name + (2) and (3), with different permissions. I guess user2 should have just one folder.

[PVince81]

@SergioBertolinSG this is another issue, not related to this one.

See #24575 and #25113

Internally the shares must be created in a duplicated manner to be able to unshare again. However at mount time, some logic needs to be adjusted to properly merge the shares together as it used to do in OC <= 8.2

[SergioBertolinSG]

OK, 👍 then.

[lock]

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