Fix filter_iter so that exception is caught

Author: schlatterbeck

roundup/backends/back_postgresql.py

@@ -593,7 +593,8 @@ def filter(self, *args, **kw):
     def filter_iter(self, *args, **kw):
         self.db.sql('savepoint sp')
         try:
-            return rdbms_common.Class.filter_iter(self, *args, **kw)
+            for v in rdbms_common.Class.filter_iter(self, *args, **kw):
+                yield v
         except psycopg2.errors.DataError as err:
             self.db.sql('rollback to savepoint sp')
             raise hyperdb.HyperdbValueError(str (err).split('\n')[0])