[views/forms] Fix EntityFieldsForm.link_to when parent entity is being created
When the parent entity is being created and the inlined form is displayed, the
parent entity has no eid yet and `peid` is usually 'A'. So int() raises a
ValueError.
Closes #4627739.
Document: cubicweb-doc
Title: CubicWeb documentation
Author: Logilab
Abstract: Some base documentation for CubicWeb users and developpers
Section: Apps/Programming
Format: HTML
Index: /usr/share/doc/cubicweb-documentation/index.html
Files: /usr/share/doc/cubicweb-documentation/*.html