Resolve dataset share checks when deleting dataset

[noah-paige]

Feature or Bugfix

• Bugfix

Detail

• Fix query to check dataset shares before deleting a dataset

The existingSharedItems property of ShareObject was not resolving correctly to a True or False value but rather to None. The impact is:

1. When checking a dataset's shares before deleting the dataset - we would not raise an exception for datasets that did in fact have existing shared items.

2. Additionally, when deleting a dataset with associated shared objects created - we would not successfully delete the associated share object and share object items and not clean up rows in the DB appropriately. This caused issues when viewing the Share Tab as the dataset does not exist but is still referenced in the outdated ShareObject and throws an error.

Relates

• User unable to submit a new share request when an earlier requested dataset was deleted #544

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[dlpzx]

lgtm, thank you!