Fix fallback color (#792)

- Make up for PR #564.
- Fixes part of #779.

Source/Painting/SvgDeferredPaintServer.cs

@@ -72,7 +72,9 @@ namespace Svg
                     _concreteServer = styleOwner.OwnerDocument.IdManager.GetElementById(DeferredId) as SvgPaintServer;
 
                     _fallbackServer = FallbackServer;
-                    if (!(_fallbackServer is SvgColourServer ||
+                    if (_fallbackServer == null)
+                        _fallbackServer = None;
+                    else if (!(_fallbackServer is SvgColourServer ||
                         (_fallbackServer is SvgDeferredPaintServer && string.Equals(((SvgDeferredPaintServer)_fallbackServer).DeferredId, "currentColor"))))
                         _fallbackServer = Inherit;
                 }
@@ -83,7 +85,7 @@ namespace Svg
         public override Brush GetBrush(SvgVisualElement styleOwner, ISvgRenderer renderer, float opacity, bool forStroke = false)
         {
             EnsureServer(styleOwner);
-            return (_concreteServer ?? _fallbackServer ?? NotSet).GetBrush(styleOwner, renderer, opacity, forStroke);
+            return _concreteServer?.GetBrush(styleOwner, renderer, opacity, forStroke) ?? _fallbackServer?.GetBrush(styleOwner, renderer, opacity, forStroke) ?? NotSet?.GetBrush(styleOwner, renderer, opacity, forStroke);
         }
 
         public override SvgElement DeepCopy()

doc/ReleaseNotes.md

@@ -20,6 +20,7 @@ The release versions are NuGet releases.
  (see [#634](https://github.com/vvvv/SVG/issues/634)
 * fixed rendering of text-anchor `middle` (see [#769](https://github.com/vvvv/SVG/issues/769)
 * fixed opacity not correctly inherited issue (see [#777](https://github.com/vvvv/SVG/issues/777) and [PR #788](https://github.com/vvvv/SVG/pull/788))
+* fixed fallback color (see [#779](https://github.com/vvvv/SVG/issues/779) and [PR #792](https://github.com/vvvv/SVG/pull/792))
 
 ## [Version 3.1.1](https://www.nuget.org/packages/Svg/3.1.1)