Track editor fails to open if a tag has multiple values

[Steve Dodier-Lazaro]

r2279

I'm getting the following traceback as soon as a tag in a track has several values. print repr(value) just before the call in the traceback gives, for instance : u'Apocalyptica\x00Sandra Nasic' if I have "Apolicalyptica" and "Sandra Nasic" artist tags.

Traceback (most recent call last):
  File "/home/steve/Exaile/BACKUP/xlgui/playlist.py", line 92, in <lambda>
    self.properties_dialog())
  File "/home/steve/Exaile/BACKUP/xlgui/playlist.py", line 114, in properties_dialog
    tracks[0])
  File "/home/steve/Exaile/BACKUP/xlgui/properties.py", line 21, in __init__
    self._populate_from_track(track)
  File "/home/steve/Exaile/BACKUP/xlgui/properties.py", line 45, in _populate_from_track
    field.set_text(value)
TypeError: GtkEntry.set_text() argument 1 must be string without null bytes, not unicode