Weird behaviour with UTF8 on Tryton client 6.4.11 with size limited Text field
I came across a weird situation in Tryton version 6.4. I have a `Text` field defined in a `Model` and limited it's size so the user gets an error when they have entered too much text.
```python
summary = fields.Text('Sale Intro Text', size=300)
```
However when the user now want to enter 'strange' characters like `éëáä` the client does strange things:
1. On windows, it's eating the the amount of the 'strange' characters away from the end of the text when saving the record.
2. On Linux, it crashes when the character is entered with
```
**
Gtk:ERROR:../gtk/gtktextbtree.c:1182:_gtk_text_btree_insert: assertion failed: (g_utf8_validate (&text[sol], chunk_len, NULL))
Bail out! Gtk:ERROR:../gtk/gtktextbtree.c:1182:_gtk_text_btree_insert: assertion failed: (g_utf8_validate (&text[sol], chunk_len, NULL))
Aborted (core dumped)
```
Removing the `size=300` allows to enter the 'strange' characters again, but now there is no limit.
It this something coming from the underlying GTK libraries? I also noticed this error seems to be gone in version 6.6
issue