[librsvg/librsvg-2.44] DrawingCtx: log when an element references a nonexistent mask

[Federico Mena Quintero <federico src gnome org>]

commit bc7bb8c1543cddf2739d9ea3efbb9a62f3746278
Author: Federico Mena Quintero <federico gnome org>
Date:   Wed Oct 24 11:39:26 2018 -0500

    DrawingCtx: log when an element references a nonexistent mask

 rsvg_internals/src/drawing_ctx.rs | 6 ++++++
 1 file changed, 6 insertions(+)
---
diff --git a/rsvg_internals/src/drawing_ctx.rs b/rsvg_internals/src/drawing_ctx.rs
index fa158398..f34dfbf5 100644
--- a/rsvg_internals/src/drawing_ctx.rs
+++ b/rsvg_internals/src/drawing_ctx.rs
@@ -461,6 +461,12 @@ impl<'a> DrawingCtx<'a> {
                                 mask.generate_cairo_mask(&node, &affine, self)
                             })
                         });
+                    } else {
+                        rsvg_log!(
+                            "element {} references nonexistent mask \"{}\"",
+                            node.get_human_readable_name(),
+                            mask,
+                        );
                     }
                 } else if opacity < 1.0 {
                     original_cr.paint_with_alpha(opacity);