EditFont's use of Curve.len was very confusing, in editmode it represented the number of characters, in object mode the number of bytes. add Curve.len_wchar and keep track of both. Also don't convert the editmode text into utf8 on every keystroke. Now this is done on exiting editmode or save - to match most other object types. This also fixes curves 'body_format' being reported with an invalid size.