Ensure form for fields created during install

Fixes #374

include/class.dynamic_forms.php

@@ -130,6 +130,7 @@ class DynamicForm extends VerySimpleModel {
             foreach ($ht['fields'] as $f) {
                 $f = DynamicFormField::create($f);
                 $f->form_id = $inst->id;
+                $f->setForm($inst);
                 $f->save();
             }
         }