Core: Options: Fix category list width

If the vertical scrollbar is invisible, it reports a width of 100
pixels. Use the width of the size hint, instead.

Task-number: QTCREATORBUG-20353
Change-Id: I3d50041788f12360a98a8f41923c6a38e23a63e3
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

src/plugins/coreplugin/dialogs/settingsdialog.cpp

@@ -316,7 +316,7 @@ public:
     QSize sizeHint() const final
     {
         int width = sizeHintForColumn(0) + frameWidth() * 2 + 5;
-        width += verticalScrollBar()->width();
+        width += verticalScrollBar()->sizeHint().width();
         return QSize(width, 100);
     }