[bug-recutils] The "size" field type treats Non-US-ASCII characters as multiple

[Mampir]

Hi!

The title should explain the issue on its own.  Here is an example:
  # -*- mode: rec -*-
  
  %rec: Text
  %type: Cyrillic size 3
  
  Cyrillic: Бъг
  
  # End of report.rec

recfix outputs:
  report.rec:6: error: value too large.  Expected a size <= 3.

The "size" field type treats "Бъг" like it's 6 characters long.