event: Make removing feedbacks more self contained

If the feedback is in our list of feedbacks disconnect signals
and drop the reference we hold.

As we have removed the signal handler that would invoke `check_ended()`
we invoke this manually when the list becomes empty.

src/fbd-event.c

@@ -361,10 +361,26 @@ fbd_event_get_feedbacks (FbdEvent *self)
 int
 fbd_event_remove_feedback (FbdEvent *self, FbdFeedbackBase *feedback)
 {
+  guint len;
+
   g_return_val_if_fail (FBD_IS_EVENT (self), 0);
 
+  if (!self->feedbacks)
+    return 0;
+
+  if (g_slist_index (self->feedbacks, feedback) >= 0) {
+    g_signal_handlers_disconnect_by_data (feedback, self);
+    /* Drop our reference, feedbacks end themselves when unref'ed */
+    g_object_unref (feedback);
+  }
+
   self->feedbacks = g_slist_remove (self->feedbacks, feedback);
-  return g_slist_length (self->feedbacks);
+
+  len = g_slist_length (self->feedbacks);
+  if (!len)
+    check_ended (self);
+
+  return len;
 }
 
 /**