Determine if a file is an icon
<p>I'm reading from an image file via <code>OpenImageFileDialog</code>, which accepts both <code>.ico</code> and bitmap file. With icons, I need to create an <code>Icon</code> object and convert it to a bitmap.</p>

<p>How can I tell whether a file is actually an icon? Just checking for an <code>.ico</code> extension seems unreliable.</p>
