Set wxSL_VERTICAL style in wxSlider demo page.

wxGTK doesn't currently take wxSL_{LEFT,RIGHT,TOP,BOTTOM} styles into account
but at least make it change the slider orientation correctly depending on them.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@62618 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

samples/widgets/slider.cpp

@@ -402,14 +402,14 @@ void SliderWidgetsPage::CreateSlider()
             break;
 
         case SliderTicks_Left:
-            flags |= wxSL_LEFT;
+            flags |= wxSL_LEFT | wxSL_VERTICAL;
             break;
 
         case SliderTicks_Bottom:
             flags |= wxSL_BOTTOM;
             break;
 
-        case SliderTicks_Right:
+        case SliderTicks_Right | wxSL_VERTICAL:
             flags |= wxSL_RIGHT;
             break;