libsaria: Check that next() returns a file

If next doesn't return a file, we shouldn't try to load something.  That
would just be silly.

libsaria/controls.py

@@ -37,7 +37,8 @@ def init2():
 def pick_next():
 	global pause_after
 	file = sources.next()
-	load(file)
+	if file != None:
+		load(file)
 	if pause_after == True:
 		pause()
 	else: