[BUG] When an unconfigured key is used, the output stops working, even on the paper tape and won't work again until reconnect

[Monniasza]

Describe the bug

A clear and concise description of what the bug is.

To Reproduce

Steps to reproduce the behavior:

1. Configure a key to be empty (not no-op)
2. Use that key
3. Write something else on that machine
4. See that nothing is written

Expected behavior
Nothing happens, and machine works without interruption

Operating system

• OS: Windows 10
• Plover Version 4.0.0dev12

Hardware
I'm using Picosteno, but I've forgot to map S1-, so the issue occurred when I wanted to write some numbers