Ensure responses are sent with empty bodies for WSGI

The previous code was meant to ensure the response was not sent until
the first byte was recevied. However, as the response_body has been
set this should be enough and ensures that empty response bodies work.

src/hypercorn/app_wrappers.py

@@ -85,7 +85,6 @@ async def handle_http(
 
     def run_app(self, environ: dict, send: Callable) -> None:
         headers: List[Tuple[bytes, bytes]]
-        headers_sent = False
         response_started = False
         status_code: Optional[int] = None
 
@@ -109,12 +108,9 @@ def start_response(
         if not response_started:
             raise RuntimeError("WSGI app did not call start_response")
 
+        send({"type": "http.response.start", "status": status_code, "headers": headers})
         try:
             for output in response_body:
-                if not headers_sent:
-                    send({"type": "http.response.start", "status": status_code, "headers": headers})
-                    headers_sent = True
-
                 send({"type": "http.response.body", "body": output, "more_body": True})
         finally:
             if hasattr(response_body, "close"):