gh-142352: pause transport before moving buffered data

Move pause_reading() ahead of the StreamReader buffer handoff in
BaseEventLoop.start_tls() for clearer sequencing.

Author: kasimov-maxim

Lib/asyncio/base_events.py

@@ -1341,6 +1341,10 @@ async def start_tls(self, transport, protocol, sslcontext, *,
             ssl_shutdown_timeout=ssl_shutdown_timeout,
             call_connection_made=False)
 
+        # Pause early so that "ssl_protocol.data_received()" doesn't
+        # have a chance to get called before "ssl_protocol.connection_made()".
+        transport.pause_reading()
+
         # gh-142352: move buffered StreamReader data to SSLProtocol
         if server_side:
             stream_reader = getattr(protocol, '_stream_reader', None)
@@ -1350,10 +1354,6 @@ async def start_tls(self, transport, protocol, sslcontext, *,
                     ssl_protocol._incoming.write(buffer)
                     buffer.clear()
 
-        # Pause early so that "ssl_protocol.data_received()" doesn't
-        # have a chance to get called before "ssl_protocol.connection_made()".
-        transport.pause_reading()
-
         transport.set_protocol(ssl_protocol)
         conmade_cb = self.call_soon(ssl_protocol.connection_made, transport)
         resume_cb = self.call_soon(transport.resume_reading)