Handle peer shutdown correctly in ipc_sendrecv_with_fds

[deanlee]

Fixes a bug in ipc_sendrecv_with_fds where a clean peer shutdown (EOF) was not handled.

• recvmsg() == 0 → peer closed the socket cleanly (EOF). (example close(fd) or shutdown(fd, SHUT_WR))
• recvmsg() == -1 with errno == ECONNRESET → connection reset unexpectedly (peer process crashed | TCP-level reset).

Details:

• When the server closes the UNIX socket cleanly, recvmsg() returns 0 to indicate EOF.
• Previous code did not handle this case, proceeding to process control messages from an empty connection.
• This could cause VisionIpcClient::connect to return true even though no valid data was received.
• The fix explicitly checks for r == 0 and handles peer shutdown gracefully.

This is a correctness/robustness fix; it can cause crashes or undefined behavior in some situations if not handled.