Fix bug with sorting of virtual columns

Certain non-local fields would raise errors when checked for sorting instructions.

datatableview/__init__.py

@@ -1,7 +1,7 @@
 # -*- coding: utf-8 -*-
 __name__ = 'datatableview'
 __author__ = 'Tim Valenta'
-__version_info__ = (0, 6, 2)
+__version_info__ = (0, 6, 3)
 __version__ = '.'.join(map(str, __version_info__))
 __date__ = '2013/11/14 2:00:00 PM'
 __credits__ = ['Tim Valenta', 'Steven Klass']

datatableview/utils.py

@@ -320,7 +320,10 @@ def _normalize_options(self, query, options):
 
                     column = options['columns'][column_index]
                     column = get_field_definition(column)
-                    is_local_field = column.fields[0] in self._model._meta.get_all_field_names()
+                    if column.fields and column.fields[0] in self._model._meta.get_all_field_names():
+                        is_local_field = True
+                    else:
+                        is_local_field = False
                     if not column.fields or len(column.fields) > 1 or not is_local_field:
                         field_name = '!{0}'.format(column_index)
 

setup.py

@@ -4,7 +4,7 @@
 from setuptools import setup, find_packages
 
 setup(name='django-datatable-view',
-      version='0.6.2',
+      version='0.6.3',
       description='This package is used in conjunction with the jQuery plugin '
                   '(http://http://datatables.net/), and supports state-saving detection'
                   ' with (http://datatables.net/plug-ins/api).  The package consists of '