ignore DUPLICATE_VALUE on sched item errors

[aheber]

Changes

Ignore duplicate value error on Schedule Items caused by sharing isolation

Issues Closed

#375

[aheber]

I wasn't able to come up with a reasonably testable pattern for this to add an Apex Test.

Manual Testing Steps:
Create another user in the org using the Minimum Profile
Add a Perm Set that grants tab, read, create, edit to Account and Contact
Assign to new minimal user
Create a DLRS Rollup in Scheduled mode with the Contact as child object and Account as parent object, save and activate
Change Sharing Settings for the Scheduled Item object so it is Private for internal users. (Most occurrences are caused by Guest users on the external Private sharing).

Create an account with your full user
Create a Contact with your full user

Using the limited user, edit the contact in a way that would cause a Scheduled item record to be created. This should throw a DUPLICATE_VALUE error on save for the limited user. With this change in place it should succeed.

To make sure other errors are still surfaced, you can create a validation rule that always returns an error. Edit the child record again to create a new Scheduled Item record, this should throw a generally standard error message in the standard way.