[gnome-system-monitor] Do not draw hidden graphs

[Robert Roth <robertroth src gnome org>]

commit 939283f555106b1e78aaf00beb01100714e208ba
Author: Robert Roth <robert roth off gmail com>
Date:   Fri Nov 6 02:29:47 2020 +0200

    Do not draw hidden graphs

 src/load-graph.cpp | 1 +
 1 file changed, 1 insertion(+)
---
diff --git a/src/load-graph.cpp b/src/load-graph.cpp
index 64a601d7..b9c939fb 100644
--- a/src/load-graph.cpp
+++ b/src/load-graph.cpp
@@ -300,6 +300,7 @@ load_graph_state_changed (GtkWidget *widget,
 {
     LoadGraph * const graph = static_cast<LoadGraph*>(data_ptr);
     force_refresh (graph);
+    graph->draw = gtk_widget_is_visible (widget);
     return TRUE;
 }