Fix layout editor not rendering after configuring layouts

how to reproduce

• go to studio modeler
• Under the Configuration menu, click on the Content Model section, then Document Types. Click on the New button, then fill as follow:
  • ID: Contract
  • Extends: File
  • Label: Contract
  • Save
• go to Designer
• under the UI menu, click in Layouts > Local Document Types > Contract
• click in the Configure Missing Layouts button
• open the create layout
• preview stays rendering and it's not shown - bug