middleware: Add isinstance check before retrieving content.

StreamingHttpResponse is inferred without the isinstance check in the
else branch. We refactor this is shorten the code and also type narrow
it appropriately.

zerver/middleware.py

@@ -2,18 +2,7 @@ import cProfile
 import logging
 import time
 import traceback
-from typing import (
-    Any,
-    AnyStr,
-    Callable,
-    Dict,
-    Iterable,
-    Iterator,
-    List,
-    MutableMapping,
-    Optional,
-    Tuple,
-)
+from typing import Any, AnyStr, Callable, Dict, Iterable, List, MutableMapping, Optional, Tuple
 from urllib.parse import urlencode
 
 from django.conf import settings
@@ -425,13 +414,10 @@ class LogRequests(MiddlewareMixin):
             else:
                 requestor_for_logs = "unauth@{}".format(get_subdomain(request) or "root")
 
-        if response.streaming:
-            assert isinstance(response, StreamingHttpResponse)
-            content_iter: Optional[Iterator[bytes]] = response.streaming_content
-            content = None
-        else:
-            content = response.content
-            content_iter = None
+        content_iter = (
+            response.streaming_content if isinstance(response, StreamingHttpResponse) else None
+        )
+        content = response.content if isinstance(response, HttpResponse) else None
 
         assert request_notes.client_name is not None and request_notes.log_data is not None
         assert request.method is not None