last-used-folder -> None crash

[Michael Schwendt]

Another crash has been reported where the code tries to set "last-used-folder" to "None" in one place where no safety check is applied:

    https://bugzilla.redhat.com/836338

backtrace:
:gconfstore.py:55:set_string:TypeError: GConf.Client.set_string() argument 2
must be string, not None
:
:Traceback (most recent call last):
: File "/usr/lib/soundconverter/python/soundconverter/ui.py", line 1254, in
on_addfolder_activate
: self.addfolderchooser.get_current_folder_uri())
: File "/usr/lib/soundconverter/python/soundconverter/gconfstore.py", line 55,
in set_string
: self.gconf.set_string(self.path(key), value)
:TypeError: GConf.Client.set_string() argument 2 must be string, not None
:
:Local variables in innermost frame:
:self: <soundconverter.ui.PreferencesDialog object at 0xb6b7128c>
:key: 'last-used-folder'
:value: None

[GautierPortet (kassoulet)]

Thank you Michael!