fix typo (#1675)

src/widgets/Scrollbar.cpp

@@ -356,10 +356,10 @@ void Scrollbar::mouseMoveEvent(QMouseEvent *event)
     {
         int delta = event->pos().y() - this->lastMousePosition_.y();
 
-        setDesiredValue(this->desiredValue_ +
+        setDesiredValue(
-                        qreal(delta) /
+            this->desiredValue_ +
-                            std::max<qreal>(0.00000002, this->trackHeight_ *
+            (qreal(delta) / std::max<qreal>(0.00000002, this->trackHeight_)) *
-                                                            this->maximum_));
+                this->maximum_);
     }
 
     this->lastMousePosition_ = event->pos();