fix common misconception about having to connect client first

Author: qwertyquerty

pypresence/baseclient.py

@@ -113,6 +113,9 @@ def send_data(self, op: int, payload: Union[dict, Payload]):
         if isinstance(payload, Payload):
             payload = payload.data
         payload = json.dumps(payload)
+
+        assert self.sock_writer is not None, "You must connect your client before sending events!"
+
         self.sock_writer.write(
             struct.pack(
                 '<II',