Viewport: Fix viewport updates being applied to shaded windows

src/gfx.cpp

@@ -1559,7 +1559,7 @@ void DrawDirtyBlocks()
 				w->flags &= ~WF_WIDGETS_DIRTY;
 			}
 
-			if (w->viewport != nullptr) {
+			if (w->viewport != nullptr && !w->IsShaded()) {
 				ViewPort *vp = w->viewport;
 				if (vp->is_drawn) {
 					vp->ClearDirty();

src/widget.cpp

@@ -2002,8 +2002,8 @@ void NWidgetViewport::UpdateViewportCoordinates(Window *w)
 	if (vp != nullptr) {
 		vp->left = w->left + this->pos_x;
 		vp->top  = w->top + this->pos_y;
-		vp->width  = this->current_x;
-		vp->height = this->current_y;
+		vp->width  = w->IsShaded() ? 0 : this->current_x;
+		vp->height = w->IsShaded() ? 0 : this->current_y;
 
 		vp->virtual_width  = ScaleByZoom(vp->width, vp->zoom);
 		vp->virtual_height = ScaleByZoom(vp->height, vp->zoom);