BUG: When painting ctkRangeSlider, the slider groove was highlighted

There was an extra highlight in the Slider groove done by
painter.drawComplexControl(QStyle::CCSlider, option); This is because the
painting assumes the slider position is valid. Disable it by setting its
position to the minimum (left).

Libs/Widgets/ctkRangeSlider.cpp

@@ -423,6 +423,7 @@ void ctkRangeSlider::paintEvent( QPaintEvent* )
 
   QStylePainter painter(this);
   option.subControls = QStyle::SC_SliderGroove;
+  option.sliderPosition = this->minimum(); // don't highlight the SliderGroove
   painter.drawComplexControl(QStyle::CC_Slider, option);
 
   option.sliderPosition = d->m_MinimumPosition;