bug #20504: fix crash when printing. r=joki

view/src/nsViewManager.cpp

@@ -2248,8 +2248,9 @@ void nsViewManager::AddRectToDirtyRegion(nsIView* aView, const nsRect &aRect) co
 	// Find a view with an associated widget. We'll transform this rect from the
 	// current view's coordinate system to a "heavyweight" parent view, then convert
 	// the rect to pixel coordinates, and accumulate the rect into that view's dirty region.
-	nsRect widgetRect = aRect;
 	nsIView* widgetView = GetWidgetView(aView);
+	if (widgetView != nsnull) {
+		nsRect widgetRect = aRect;
 		ViewToWidget(aView, widgetView, widgetRect);
 
 		// Get the dirty region associated with the widget view
@@ -2259,6 +2260,7 @@ void nsViewManager::AddRectToDirtyRegion(nsIView* aView, const nsRect &aRect) co
 			dirtyRegion->Union(widgetRect.x, widgetRect.y, widgetRect.width, widgetRect.height);
 		}
 	}
+}
 
 void nsViewManager::UpdateTransCnt(nsIView *oldview, nsIView *newview)
 {