configuring --without-sound leaves instance attribute undefined

[skids]

I build from svn trunk 7906, configured --without-sound, and in order to get things operational, had to add a

hidden_options["sound_source"] = None

in xpra/scripts/main.py

line 465ish

Otherwise python complains about accessing this attribute later on around line 670ish.

I have no clue if that's the right fix.

[Antoine Martin]

It is totally the right fix and has been applied in r7920. Thanks!