Fix a db_to_form_package_schema() crash

When db_to_form_package_schema() was in use (e.g. when an IDatasetForm
plugin with a db_to_form_schema() method based on
db_to_form_package_schema() was active) then try to edit a package that
has some resources would crash with a 400 Bad Request.

Extremely difficult to debug.

This seems to fix it.

ckan/logic/schema.py

@@ -195,6 +195,7 @@ def db_to_form_package_schema():
     # TODO: Fix this elsewhere so we don't need to workaround it here.
     schema['resources'].update({
         'created': [ckan.lib.navl.validators.ignore_missing],
+        'position': [not_empty],
         'last_modified': [ckan.lib.navl.validators.ignore_missing],
         'cache_last_updated': [ckan.lib.navl.validators.ignore_missing],
         'webstore_last_updated': [ckan.lib.navl.validators.ignore_missing],