[librsvg/librsvg-2.44] Add FilterError::ChildNodeInError

[Federico Mena Quintero <federico src gnome org>]

commit 085b6ad511253a42c754ce6cdfe8061cedd7ddc5
Author: Ivan Molodetskikh <yalterz gmail com>
Date:   Tue Sep 25 11:34:04 2018 +0300

    Add FilterError::ChildNodeInError

 rsvg_internals/src/filters/error.rs | 3 +++
 1 file changed, 3 insertions(+)
---
diff --git a/rsvg_internals/src/filters/error.rs b/rsvg_internals/src/filters/error.rs
index 1b5f61ca..2a4599fe 100644
--- a/rsvg_internals/src/filters/error.rs
+++ b/rsvg_internals/src/filters/error.rs
@@ -19,6 +19,8 @@ pub enum FilterError {
     InvalidLightSourceCount,
     /// A lighting filter input surface is too small.
     LightingInputTooSmall,
+    /// Child node was in error.
+    ChildNodeInError,
 }
 
 impl Error for FilterError {
@@ -32,6 +34,7 @@ impl Error for FilterError {
             FilterError::LightingInputTooSmall => {
                 "lighting filter input surface is too small (less than 2×2 pixels)"
             }
+            FilterError::ChildNodeInError => "child node was in error",
         }
     }