Work around bogus warning C4701: potentially uninitialized local variable

Change-Id: I9c5d9c53785828b3535c960f826ccd3720b2e4c3

sdext/source/presenter/PresenterPaneBorderPainter.cxx

@@ -550,7 +550,7 @@ void PresenterPaneBorderPainter::Renderer::PaintTitle (
     case RendererPaneStyle::Anchor::Right:
         nX = rInnerBox.X + rInnerBox.Width - nTextWidth;
         break;
-    case RendererPaneStyle::Anchor::Center:
+    default: // RendererPaneStyle::Anchor::Center
         nX = rInnerBox.X + (rInnerBox.Width - nTextWidth)/2;
         break;
     }