fix gdi resource leak with unreleased virtual device

(copycat Markus https://cgit.freedesktop.org/libreoffice/core/commit/?id=289711c2a469bfbe06aef3b3870b65f9c788f56d)

Change-Id: I3974609559dd44257d7c3e9e9544348d622953f6
Reviewed-on: https://gerrit.libreoffice.org/37586Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Julien Nabet <serval2412@yahoo.fr>

cui/source/options/optchart.cxx

@@ -43,7 +43,7 @@ void SvxDefaultColorOptPage::InsertColorEntry(const XColorEntry& rEntry, sal_Int
     const StyleSettings& rStyleSettings = Application::GetSettings().GetStyleSettings();
     Size aImageSize = rStyleSettings.GetListBoxPreviewDefaultPixelSize();
 
-    VclPtr<VirtualDevice> xDevice = VclPtr<VirtualDevice>::Create();
+    ScopedVclPtrInstance<VirtualDevice> xDevice;
     xDevice->SetOutputSize(aImageSize);
     const ::tools::Rectangle aRect(Point(0, 0), aImageSize);
     xDevice->SetFillColor(rColor);