[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.
../../doc/book usr/share/doc/cubicweb-documentation
../../doc/html usr/share/doc/cubicweb-documentation
../../debian/cubicweb-doc usr/share/doc-base/cubicweb-doc