Run(): clear previous timer id if needed

Fixes dunst-project#1196

src/dunst.c

@@ -101,6 +101,8 @@ static gboolean run(void *data)
  draw();
  output->win_show(win);
 
+ bool timeout_set = true;
+
  gint64 timeout_at = queues_get_next_datachange(now);
  if (timeout_at != -1) {
  // Previous computations may have taken time, update `now`
@@ -117,12 +119,19 @@ static gboolean run(void *data)
  if (next_timeout != 0) {
  g_source_remove(next_timeout_id);
  }
+ timeout_set = true;
  next_timeout_id = g_timeout_add(sleep/1000, run, NULL);
  next_timeout = timeout_at;
  }
  }
  }
 
+ if(!timeout_set) {
+ // If no new timeout was set this time, clear up te timer id
+ next_timeout = 0;
+ next_timeout_id = 0;
+ }
+
  /* If the execution got triggered by g_timeout_add,
  * we have to remove the timeout (which is actually a
  * recurring interval), as we have set a new one