In FormDef.get_detailed_email_form skip non-input fields

Skipped field classes are: TitleField, SubtitleField, PageField and
CommentField.

Those classes do not have a working get_rst_view_value method, it breaks
the logic of get_detailed_email_form.

wcs/formdef.py

@@ -413,6 +413,9 @@ class FormDef(StorableObject):
 
         for field in self.fields:
             data = formdata.data
+            if isinstance(field, (SubtitleField, TitleField, CommentField,
+                PageField)):
+                continue
             if data.get(field.id) is None:
                 continue
             details.append(_('%s:') % field.label)