Prevent Whoosh from erroring if the end_offset is less than or eq…

…ual to 0. Thanks to zifot for the report!

haystack/backends/whoosh_backend.py

@@ -333,6 +333,11 @@ def search(self, query_string, sort_by=None, start_offset=0, end_offset=None,
                     'hits': 0,
                 }
 
+            # Prevent against Whoosh throwing an error. Requires an end_offset
+            # greater than 0.
+            if not end_offset is None and end_offset <= 0:
+                end_offset = 1
+
             raw_results = searcher.search(parsed_query, limit=end_offset, sortedby=sort_by, reverse=reverse)
 
             # Handle the case where the results have been narrowed.

tests/whoosh_tests/tests/whoosh_backend.py

@@ -313,6 +313,10 @@ def test_slicing(self):
         self.assertEqual([result.pk for result in page_1['results']], [u'%s' % i for i in xrange(1, 21)])
         self.assertEqual(len(page_2['results']), 3)
         self.assertEqual([result.pk for result in page_2['results']], [u'21', u'22', u'23'])
+
+        # This used to throw an error.
+        page_0 = self.sb.search(u'*', start_offset=0, end_offset=0)
+        self.assertEqual(len(page_0['results']), 1)
 
     def test_scoring(self):
         self.sb.update(self.smmi, self.sample_objs)