set value of player not only gui (but that should have been enough)

src/config.py

@@ -300,7 +300,9 @@ class PreferencesWindow:
 			for command in commands:
 				if helpers.is_in_path(command):
 					self.xml.get_widget('soundplayer_entry').set_text(command)
+					gajim.config.set('soundplayer', command)
 					break
+		
 
 		#sounds treeview
 		self.sound_tree = self.xml.get_widget('sounds_treeview')