curds: Make sure we're properly setting prev / next pointers

I noticed that the toplevel playlist siblings were always set to None,
so make sure we're properly setting these so they can be used.

Signed-off-by: Anna Schumaker <Anna@NoWheyCreamery.com>

curds/playlist/node.py

@@ -11,12 +11,12 @@ class PlaylistNode:
         self.prev_child = None
 
     def __link_children__(self, a, b, c):
-        if a:
+        if a != None:
             a.next_child = b
         b.parent = self
         b.prev_child = a
         b.next_child = c
-        if c:
+        if c != None:
             c.prev_child = b
 
     def __lt__(self, rhs):

curds/playlist/test_manager.py

@@ -67,6 +67,9 @@ class TestPlaylistManager(unittest.TestCase):
         self.assertEqual(self.playman.nth_child(4), self.playman.lookup("Decades"))
         self.assertEqual(self.playman.nth_child(5), self.playman.lookup("Libraries"))
 
+        for i, plist in enumerate(self.playman.children):
+            self.assertEqual(plist.next_child, self.playman.nth_child(i + 1))
+
         self.assertEqual(self.playman.name,   "Root")
         self.assertEqual(self.playman.current, [ self.playman.lookup("Collection") ])
         self.assertEqual(self.playman.track,   None)