Fix infinite recursion with Delivery_viewSolveDivergenceDialog. Do not enable (and so, do not try to validate) the solver configuration formbox if there is no solver.

Also make changes to make these kinds of errors easier to diagnose by having an explicitly invalid value as a fallback when the TALES expression fails.

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@44142 20353a03-c40f-0410-a6d1-a30d3c3de9de