False positive of missing referenced (child) layer

[harminius]

Fixes https://odoo.lutraconsulting.co.uk/odoo/my-tickets/16926

Issue:

When a child layer was removed from the project and then re-added, a new layer ID is generated. This new ID does not match the one stored in the field config of the reference (parent) layer.

Adding new features with the relation works fine, as QGS has a special method for this which falls back to the layer name and its source when it fails to find a matching layer ID.

Let's follow the standard method, which was introduced in version 3.2.

original warning:

[MarcelGeo]

@RastoHu https://github.com/MerginMaps/qgis-plugin/actions/runs/33482414931

[IvaKuklica]

Testing note:

Test passed ✅.

Reproduced the reported false-positive "Referenced table is missing from the project" warning using a layer field with a Value Relation widget pointing to another layer — the referenced layer was removed from the project and re-added from the same source, causing the widget's layer reference to break and trigger the warning even though the layer was present under the same name/source.

Retested the exact same steps on the updated plugin build with the fix applied — the warning no longer appears.