Fix missing non-ascii symbols in window titles in  windowname widget

It seems that sometimes, when window title contains ascii and non-ascii chars, GetProperty returns truncated window title with half of non-ascii symbol on the end, like here:
```python
In [7]: print "фуу"[:5]
фуÑ
```
And when it occurs function scrub_to_utf8 remove ALL non-ascii chars in title and it looks weird. I suggest just preserve all symbols except symbols with problems.