braille_alphabets level5 doesn't work: one digit ints messed with chars

[Aapo Rantalainen]

Gcompris: 12.01-0ubuntu1
Activity: braille_alphabet ("Discover the braille system")
Go to level 5. Level can't be played.

 Traceback (most recent call last):
  File "/usr/share/gcompris/python/braille_alphabets.py", line 132, in set_level
    self.display_level(self.gcomprisBoard.level)
  File "/usr/share/gcompris/python/braille_alphabets.py", line 256, in display_level
    self.braille_cell(level)
  File "/usr/share/gcompris/python/braille_alphabets.py", line 293, in braille_cell
    self.play_letter(self.random_letter)
  File "/usr/share/gcompris/python/braille_alphabets.py", line 289, in play_letter
    filename = 'voices/$LOCALE/alphabet/U%04X.ogg' % ord(letter.lower())
AttributeError: 'int' object has no attribute 'lower'

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This makes it playable, but not winnable (it doesn't recognise correct answer)
src/braille_alphabets-activity/braille_alphabets.py
     elif(level == 5):
         self.show_play_button()
- chars = ['0','1','2','3','4','5','6','7','8','9']
+ chars = [0,1,2,3,4,5,6,7,8,9]
         self.gcomprisBoard.number_of_sublevel = len(chars)