PVS-Studio warning V595 for KDE4

void KDoubleNumInput::spinBoxChanged(double val)
{
  ....
  const double slidemin = priv->slider->minimum();      //<==
  const double slidemax = priv->slider->maximum();      //<==
  ....
  if (priv->slider) {                                   //<==
    priv->slider->blockSignals(true);
    priv->slider->setValue(qRound(slidemin + rel * (....)));
    priv->slider->blockSignals(false);
  }
}

This suspicious code was found in KDE4 project by PVS-Studio static code analyzer.
Warning message is:
V595 The 'priv->slider' pointer was utilized before it was verified against nullptr. Check lines: 786, 792. knuminput.cpp 786

PVS-Studio is a static analyzer for detecting bugs in the source code of applications written in C, C++, C++11, C++/CX. Site: http://www.viva64.com/en/pvs-studio/