title: Why isn't QToolButton's icon displayed?
body: <p>I meet the problem, so I take a test at MainWindow, the problem remains the same.
  Here is the code in "MainWindow::MainWindow(QWidget *parent)..."</p>
  
  <pre><code>QToolButton* bt = new QToolButton(this);
  bt-&gt;setIcon(QIcon(":/te.png"));
  bt-&gt;setToolButtonStyle(Qt::ToolButtonIconOnly);
  bt-&gt;show();
  </code></pre>
  
  <p>It looks like:
      <img src="https://i.stack.imgur.com/VMGdQ.png" alt="enter image description here"></p>
  
  <p>My resource file is like this:
      <img src="https://i.stack.imgur.com/M24Ax.png" alt="enter image description here"></p>