Can't switch to monitor with rr=record
Description of problem:
With the above args, while the guest is paused (either because I haven't attached GDB yet, or because I've halted execution in GDB), it's not possible to switch to the QEMU monitor.

I don't reproduce this issue with `QEMU emulator version 8.2.4 (Debian 1:8.2.4+ds-1+build1)` but I do with 9.2 and master (built from source).

AFAICT, the monitor is working - if I just set `-monitor stdio` instead of `-serial mon:stdio` I can use it, including when the VM is paused. But the multiplexing doesn't work.
Steps to reproduce:
1. Run the above
2. Ctrl-A, c