[bug] taking a screengrab with nano open causes error

when i try to do a screen grab, which is shift + win + s, it causes an error
```
/usr/bin/nano.lua:703: attempt to index a nil value (field '?'):
stack traceback:
  /usr/bin/nano.lua:703: in main chunk
  (...tail calls...)
  [C]: in function 'xpcall'
  machine:798: in global 'xpcall'
  /lib/process.lua:63: in function </lib/process.lua:59>
```