[1.6.x] Fixed #18592 -- Prevented crash when accessing MySQL _last_executed

Thanks reames at asymmetricventures.com for the report.
Backport of 59b0c48ce from master.

django/db/backends/mysql/base.py

@@ -284,7 +284,7 @@ class DatabaseOperations(BaseDatabaseOperations):
         # With MySQLdb, cursor objects have an (undocumented) "_last_executed"
         # attribute where the exact query sent to the database is saved.
         # See MySQLdb/cursors.py in the source distribution.
-        return force_text(cursor._last_executed, errors='replace')
+        return force_text(getattr(cursor, '_last_executed', None), errors='replace')
 
     def no_limit_value(self):
         # 2**64 - 1, as recommended by the MySQL documentation

tests/backends/tests.py

@@ -164,6 +164,17 @@ class DateQuotingTest(TestCase):
 @override_settings(DEBUG=True)
 class LastExecutedQueryTest(TestCase):
 
+    def test_last_executed_query(self):
+        """
+        last_executed_query should not raise an exception even if no previous
+        query has been run.
+        """
+        cursor = connection.cursor()
+        try:
+            connection.ops.last_executed_query(cursor, '', ())
+        except Exception:
+            self.fail("'last_executed_query' should not raise an exception.")
+
     def test_debug_sql(self):
         list(models.Reporter.objects.filter(first_name="test"))
         sql = connection.queries[-1]['sql'].lower()