Fixed CVE-2019-14234 -- Protected JSONField/HStoreField key and index lookups against SQL injection.

Thanks to Sage M. Abdullah for the report and initial patch.
Thanks Florian Apolloner for reviews.

tests/postgres_tests/test_hstore.py

@@ -1,8 +1,9 @@
 import json
 
 from django.core import checks, exceptions, serializers
+from django.db import connection
 from django.forms import Form
-from django.test.utils import isolate_apps
+from django.test.utils import CaptureQueriesContext, isolate_apps
 
 from . import PostgreSQLSimpleTestCase, PostgreSQLTestCase
 from .models import HStoreModel, PostgreSQLModel
@@ -185,6 +186,18 @@ class TestQuerying(PostgreSQLTestCase):
             self.objs[:2]
         )
 
+    def test_key_sql_injection(self):
+        with CaptureQueriesContext(connection) as queries:
+            self.assertFalse(
+                HStoreModel.objects.filter(**{
+                    "field__test' = 'a') OR 1 = 1 OR ('d": 'x',
+                }).exists()
+            )
+        self.assertIn(
+            """."field" -> 'test'' = ''a'') OR 1 = 1 OR (''d') = 'x' """,
+            queries[0]['sql'],
+        )
+
 
 @isolate_apps('postgres_tests')
 class TestChecks(PostgreSQLSimpleTestCase):