Ensure django database wrappers always have a connection before creating a cursor

Only used during ocrpus export. The .using() calls work properly.

I guess the low-level code expect that DB to be used at least once before calling the .cursor()

arkindex/documents/export/__init__.py

@@ -54,7 +54,7 @@ def run_pg_query(query, source_db):
     db = connections[source_db]
 
     # Make sure a connection is open and available for export databases
-    if db != "default" and db.connection is None:
+    if source_db != "default" and db.connection is None:
         db.connect()
 
     with db.create_cursor(name=str(uuid.uuid4())) as pg_cursor: