When sway crashes a swaybar process is sometimes left behind running at
100% CPU. This was caused by the swaybar trying to retrieve an IPC
response from the closed sway socket.
This patch fixes the problem by aborting when the socket has been closed
(recv return 0).
Fix#528
Makes `ipc_recv_response` return a struct with size, type and payload
rather than just the payload string.
This is useful if the type has to be checked on the client.
