LibHTML: Always fill the entire paint event rect with background

And do the filling before translating the painter.

This fixes a bug where scrolling down in the Help app would render the
bottom part of the page with a different background color.

Libraries/LibHTML/HtmlView.cpp

@@ -85,11 +85,11 @@ void HtmlView::paint_event(GPaintEvent& event)
         return;
     }
 
+    painter.fill_rect(event.rect(), m_document->background_color());
+
     painter.translate(frame_thickness(), frame_thickness());
     painter.translate(-horizontal_scrollbar().value(), -vertical_scrollbar().value());
 
-    painter.fill_rect(rect(), m_document->background_color());
-
     RenderingContext context { painter };
     m_layout_root->render(context);
 }