[librsvg] rsvg_handle_render_cairo_sub(): Traverse and ref ancestors correctly

[Federico Mena Quintero <federico src gnome org>]

commit 6d993e990fcadeec6d52e5997178c2e3fe57dfa1
Author: Federico Mena Quintero <federico gnome org>
Date:   Thu Mar 16 19:05:10 2017 -0600

    rsvg_handle_render_cairo_sub(): Traverse and ref ancestors correctly
    
    We get a new reference from rsvg_node_get_parent(); this wasn't being
    used correctly.

 rsvg-cairo-render.c |    4 +++-
 1 files changed, 3 insertions(+), 1 deletions(-)
---
diff --git a/rsvg-cairo-render.c b/rsvg-cairo-render.c
index 1afa60c..262a213 100644
--- a/rsvg-cairo-render.c
+++ b/rsvg-cairo-render.c
@@ -233,8 +233,10 @@ rsvg_handle_render_cairo_sub (RsvgHandle * handle, cairo_t * cr, const char *id)
         return FALSE;
 
     if (drawsub) {
+        drawsub = rsvg_node_ref (drawsub);
+
         while (drawsub != NULL) {
-            draw->drawsub_stack = g_slist_prepend (draw->drawsub_stack, rsvg_node_ref (drawsub));
+            draw->drawsub_stack = g_slist_prepend (draw->drawsub_stack, drawsub);
             drawsub = rsvg_node_get_parent (drawsub);
         }
     }