2869 Fixes problem with invalid data being passed to solr.

The feeds take a page number from the query string and use it to determine the
start position in the list.  Occassionally this is 0 and code around line 441
then decrement and then multiply this number, generating a start number less than
0 which solr chokes on.

ckan/controllers/feed.py

@@ -432,7 +432,7 @@ def _parse_url_params(self):
         """
 
         try:
-            page = int(request.params.get('page', 1))
+            page = int(request.params.get('page', 1)) or 1
         except ValueError:
             abort(400, ('"page" parameter must be an integer'))