If a client is subscribed and sends a subsequent ipc command which
causes event updates, then those event updates override the
`client->current_command` and send the incorrect type for the payload
associated with the command.
Example:
SUBSCRIBE {window}
RUN_COMMAND focus -> PAYLOAD_TYPE is 0x80000002 for window events
Therefore, we decouple the `client->current_command` by passing it as an
argument to the ipc_send_reply function, avoiding a data race. The same
is done for the `client->payload_length` as a precautionary measure for
the same reason.
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