fix(objection): table name 'xxx' specified more than once

[MoJo2600]

When a relation was already joined with withGraphJoined, ucast was adding the relation a second time. Now a check for the relation is performed.

fixes #17

[MoJo2600]

Is there a place to add unit tests for this functionality? I tried pnpm test but it told me that test was not found.

[stalniy]

tests lives in a package folder.

[stalniy]

https://github.com/stalniy/ucast/blob/master/packages/sql/spec/objection.spec.ts