Allow NULL callback for deregister

src/cubeb.c

@@ -384,7 +384,7 @@ int cubeb_stream_device_destroy(cubeb_stream * stream,
 int cubeb_stream_register_device_changed_callback(cubeb_stream * stream,
                                                   cubeb_device_changed_callback device_changed_callback)
 {
-  if (!stream || !device_changed_callback) {
+  if (!stream) {
     return CUBEB_ERROR_INVALID_PARAMETER;
   }
 

src/cubeb_audiounit.c

@@ -479,8 +479,10 @@ audiounit_add_listener(cubeb_stream * stm, AudioDeviceID id, AudioObjectProperty
 }
 
 OSStatus
-audiounit_remove_listener(cubeb_stream * stm, AudioDeviceID id, AudioObjectPropertySelector selector,
-    AudioObjectPropertyScope scope, AudioObjectPropertyListenerProc listener)
+audiounit_remove_listener(cubeb_stream * stm, AudioDeviceID id,
+                          AudioObjectPropertySelector selector,
+                          AudioObjectPropertyScope scope,
+                          AudioObjectPropertyListenerProc listener)
 {
   AudioObjectPropertyAddress address = {
       selector,