CDC-ACM locks up when closing terminal on host

Steps to reproduce:

1. Reset card10 (firmware @ 3ccec228)
2. Open debugger terminal (picocom -b 115200 /dev/ttyACM0)
3. Open CDC-ACM terminal (picocom -b 115200 /dev/ttyACM1)
4. Close CDC-ACM terminal (Press ^A^Q)
5. Paste a long text into debugger terminal

Observation:

The debugger terminal becomes unresponsive. Under the hood, Epicardium is spinning in MAXUSB's acm_write because its internal FIFO-buffer (129 bytes) if full and not emptied by the host.