LibWeb: Only auto-reschedule HTML::EventLoop when there are runnables

HTML::EventLoop tries to reschedule itself when there are more tasks in
any of its queues, but let's not do it if none of them are runnable.

Userland/Libraries/LibWeb/HTML/EventLoop/TaskQueue.cpp

@@ -33,4 +33,13 @@ OwnPtr<Task> TaskQueue::take_first_runnable()
     return nullptr;
 }
 
+bool TaskQueue::has_runnable_tasks() const
+{
+    for (auto& task : m_tasks) {
+        if (task->is_runnable())
+            return true;
+    }
+    return false;
+}
+
 }