[1.5.x] Revert "Fixed #19895 -- Made second iteration over invalid queryset raise an exception too"

This reverts commit d1e87eb3ba.
This commit was the cause of a memory leak. See ticket for more details.
Thanks Anssi Kääriäinen for identifying the source of the bug.

django/db/models/query.py

@@ -102,7 +102,7 @@ class QuerySet(object):
             len(self)
 
         if self._result_cache is None:
-            self._iter = self._safe_iterator(self.iterator())
+            self._iter = self.iterator()
             self._result_cache = []
         if self._iter:
             return self._result_iter()
@@ -337,18 +337,6 @@ class QuerySet(object):
 
             yield obj
 
-    def _safe_iterator(self, iterator):
-        # ensure result cache is cleared when iterating over a queryset
-        # raises an exception
-        try:
-            for item in iterator:
-                yield item
-        except StopIteration:
-            raise
-        except Exception:
-            self._result_cache = None
-            raise
-
     def aggregate(self, *args, **kwargs):
         """
         Returns a dictionary containing the calculations (aggregation)

tests/modeltests/basic/tests.py

@@ -2,7 +2,7 @@ from __future__ import absolute_import, unicode_literals
 
 from datetime import datetime
 
-from django.core.exceptions import ObjectDoesNotExist, MultipleObjectsReturned, FieldError
+from django.core.exceptions import ObjectDoesNotExist, MultipleObjectsReturned
 from django.db.models.fields import Field, FieldDoesNotExist
 from django.test import TestCase, skipIfDBFeature, skipUnlessDBFeature
 from django.utils import six
@@ -639,8 +639,3 @@ class ModelTest(TestCase):
         Article.objects.bulk_create([Article(headline=lazy, pub_date=datetime.now())])
         article = Article.objects.get()
         self.assertEqual(article.headline, notlazy)
-
-    def test_invalid_qs_list(self):
-        qs = Article.objects.order_by('invalid_column')
-        self.assertRaises(FieldError, list, qs)
-        self.assertRaises(FieldError, list, qs)