[1.0.X] Applying a limit to a queryset that already had an upper limit of 0

wasn't working properly.

Backport of r9201 from trunk.


git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.0.X@9204 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/db/models/sql/query.py

@@ -1491,12 +1491,12 @@ class Query(object):
         clamped to any existing high value.
         """
         if high is not None:
-            if self.high_mark:
+            if self.high_mark is not None:
                 self.high_mark = min(self.high_mark, self.low_mark + high)
             else:
                 self.high_mark = self.low_mark + high
         if low is not None:
-            if self.high_mark:
+            if self.high_mark is not None:
                 self.low_mark = min(self.high_mark, self.low_mark + low)
             else:
                 self.low_mark = self.low_mark + low

tests/regressiontests/queries/models.py

@@ -862,6 +862,8 @@ used in lookups.
 Bug #7698 -- People like to slice with '0' as the high-water mark.
 >>> Item.objects.all()[0:0]
 []
+>>> Item.objects.all()[0:0][:10]
+[]
 
 Bug #7411 - saving to db must work even with partially read result set in
 another cursor.