Fix automated search form layout configuration with custom schemas

Steps to reproduce:

• Create a custom document, "Contract" with it's own schema, including a Date field, "signatureDate", and a complex field, "client" with several subfields including a String field, "lastName".
• Create a page provider, "otherContracts" with the following query filter:

  ecm:mixinType != 'HiddenInNavigation' AND ecm:isVersion = 0 AND ecm:isTrashed = 0 AND ecm:primaryType='Contract'
  

• Add an aggregate on dc:created
• Add a predicate on the lastName field of the contract's "client" field.
• In Designer, under Layouts, click on the otherContracts page provider.
• From the main view, click on the form layout.
  => Error appears:

  Field 'contract_client' not found in schema undefined
  Field 'contract_client' not found in schema undefined
  Field 'contract_client' not found in schema undefined
  Field 'contract_client' not found in schema undefined
  Variable 'contract_signatureDate_agg' is not defined in the search document model
  Field 'contract_client' not found in schema undefined
  Field 'contract_client' not found in schema undefined
  Field 'contract_client' not found in schema undefined
  Field 'contract_client' not found in schema undefined
  Variable 'contract_signatureDate_agg' is not defined in the search document model

It seems that after 2-3 minutes of waiting, the fields appear under the error message. Then clicking on Save removes the error messages.