Exit receive loop on IOError or unhandled exceptions

May help with #4088.

telethon/network/connection/connection.py

@@ -253,7 +253,8 @@ async def disconnect(self):
         Disconnects from the server, and clears
         pending outgoing and incoming messages.
         """
-        self._connected = False
+        if not self._connected:
+            return
 
         await helpers._cancel(
             self._log,
@@ -278,6 +279,8 @@ async def disconnect(self):
                     # * ConnectionResetError
                     self._log.info('%s during disconnect: %s', type(e), e)
 
+        self._connected = False
+
     def send(self, data):
         """
         Sends a packet of data through this connection mode.
@@ -333,6 +336,7 @@ async def _recv_loop(self):
                 except (IOError, asyncio.IncompleteReadError) as e:
                     self._log.warning('Server closed the connection: %s', e)
                     await self._recv_queue.put((None, e))
+                    await self.disconnect()
                 except InvalidChecksumError as e:
                     self._log.warning('Server response had invalid checksum: %s', e)
                     await self._recv_queue.put((None, e))
@@ -342,6 +346,7 @@ async def _recv_loop(self):
                 except Exception as e:
                     self._log.exception('Unexpected exception in the receive loop')
                     await self._recv_queue.put((None, e))
+                    await self.disconnect()
                 else:
                     await self._recv_queue.put((data, None))
         except asyncio.CancelledError: