- afedrinet_io.c open_rx_udp: use snprintf so a long ip string cannot
overflow the 128-byte stack buffer.
- quisk.c set_multirx_mode, set_multirx_freq: reject a negative index.
- quisk.c set_multirx_play_channel: treat a negative channel like an
out-of-range one.
- quisk.c measure_freq: keep ipeak inside [1, fft_size - 2] so that
fft_average[ipeak - 1] and fft_average[ipeak + 1] stay in bounds when
no peak is found.
- quisk.c record_app: free the previous multirx_fft_next_samples buffer
before allocating a new one, like fft_window and current_graph.
