CPU usage while GUI inactive

# Problem description
Noticed that since version 0.11.0 the "Hello Dialog" example application from the README file, uses a tiny bit of CPU (~0,13%), while it used to be 0.00%.
After some trial and error, I found out that the commit introducing this extra CPU usage is 88d2fb1f46833e498a78d8abdcba457c5ed4ae61 with commit message "Simplifies backend input".

# Environment
* Operating system: MacOS 11.1 on MacBook Air (M1, 2020). Similar behavior seen on Debian Buster 10.7
* Backend used: ncurses 5.7
* Current locale
```
LANG=""
LC_COLLATE="C"
LC_CTYPE="UTF-8"
LC_MESSAGES="C"
LC_MONETARY="C"
LC_NUMERIC="C"
LC_TIME="C"
LC_ALL=
```
* Cursive version from git (commit: 88d2fb1f46833e498a78d8abdcba457c5ed4ae61)