showbase: Fix import of Loader if AudioLoadRequest is not available

direct/src/showbase/Loader.py

@@ -5,7 +5,6 @@ sound, music, shaders and fonts from disk.
 __all__ = ['Loader']
 
 from panda3d.core import (
-    AudioLoadRequest,
     ConfigVariableBool,
     Filename,
     FontPool,
@@ -977,6 +976,8 @@ class Loader(DirectObject):
         just as in loadModel(); otherwise, the loading happens before
         loadSound() returns."""
 
+        from panda3d.core import AudioLoadRequest
+
         if not isinstance(soundPath, (tuple, list, set)):
             # We were given a single sound pathname or a MovieAudio instance.
             soundList = [soundPath]