[librsvg] marker.rs: Don't render markers if they are zero-sized, per the spec

[Federico Mena Quintero <federico src gnome org>]

commit 556fb62786bab88e4d08ca996e655cf9fb48e3e1
Author: Federico Mena Quintero <federico gnome org>
Date:   Tue Oct 3 10:18:29 2017 -0500

    marker.rs: Don't render markers if they are zero-sized, per the spec

 rust/src/marker.rs | 5 +++++
 1 file changed, 5 insertions(+)
---
diff --git a/rust/src/marker.rs b/rust/src/marker.rs
index 908fc14..5e12ef8 100644
--- a/rust/src/marker.rs
+++ b/rust/src/marker.rs
@@ -119,6 +119,11 @@ impl NodeMarker {
         let marker_width = self.width.get ().normalize (draw_ctx);
         let marker_height = self.height.get ().normalize (draw_ctx);
 
+        if double_equals(marker_width, 0.0) || double_equals(marker_height, 0.0) {
+            // markerWidth or markerHeight set to 0 disables rendering of the element
+            // https://www.w3.org/TR/SVG/painting.html#MarkerWidthAttribute
+            return;
+        }
         let mut affine = drawing_ctx::get_current_state_affine (draw_ctx);
         affine.translate (xpos, ypos);