Fix wrong slider position

If you change the frame unit in the widget, the slider did not stay
on the right position, because the value was updated, but the range
of the slider was (apparently) not.
Not sure why it was't done in the code a few lines earlier.

src/gui/qgstemporalcontrollerwidget.cpp

@@ -301,6 +301,7 @@ void QgsTemporalControllerWidget::updateFrameDuration()
     mSlider->setValue( mNavigationObject->currentFrameNumber() );
   }
   mSlider->setRange( 0, mNavigationObject->totalFrameCount() - 1 );
+  mSlider->setValue( mNavigationObject->currentFrameNumber() );
 }
 
 void QgsTemporalControllerWidget::setWidgetStateFromProject()