Allow ARender advanced search without annotations

Steps to reproduce:

• Create a File document with PDF as the main file content.
• Navigate to Annotations tab.
• Click on Advanced Search tab.
  => No buttons are displayed in the search form.
  => Cannot search document.

Workaround:

• Add an annotation and wait for autosave.
• Go to Advanced Search tab.
  => Buttons are displayed.
  => Search can be performed.
• Delete annotation.
  => Search can still be performed.