title: PyQt5: QDoubleSpinBox does not allow negative numbers
body: <p>for some strange reasons I have trouble making my QDoubleSpinBoxes accept negative values. I've changed the range accordingly but the minimum still remains at 0 (default value). I don't have any issues involving negative numbers with QSpinBoxes, though. I find this very odd and I really can't figure out the issue here...</p>
  
  <p>For example:</p>
  
  <pre><code>self.setMinimum(1.175494e-38)
  self.setValue(-1.0)
  </code></pre>
  
  <p>... would actually change to 0.0 instead...</p>
  
  <p>Thanks in advance!</p>