title: PyQt5 QPixmap is Null with valid file
body: <p>I am trying to load an icon into a tool button. I need to first create a pixmap so I can add it to the QIcon, which then is added to the tool button. However, the pixmap is always null and nothing gets displayed on the tool button except for the default text of "..."</p>
  
  <p>Take a look at this    </p>
  
  <pre><code>file = ":/icons/refresh.jpg"
  if QtCore.QFile.exists(file):
      print("File exists")
  else:
      print("Does not exist")
  pixmap = QtGui.QPixmap(file)
  print(pixmap.isNull())
  
  &gt;&gt;&gt;File exists
  &gt;&gt;&gt;True
  </code></pre>
  
  <p>Why is the pixmap not being created when a valid file is given?</p>
  
  <p>I am running Python 3.4 in a virtualenv with PyQt5 v5.5 on Windows 10</p>