VerticalTabs - Accept click event on tree collapse

Very often when the tree collapse/expand button was pressed apart from
expected function the dragging of the tab group started.

Signed-off-by: Juraj Oravec <jurajoravec@mailo.com>

src/plugins/VerticalTabs/tabtreeview.cpp

@@ -226,6 +226,8 @@ bool TabTreeView::viewportEvent(QEvent *event)
                 } else {
                     expand(m_pressedIndex);
                 }
+                me->accept();
+                return true;
             } else if (m_pressedButton == NoButton && tab) {
                 tab->makeCurrentTab();
             }