Account for rounding errors in gradient stop positions

- if the first/last value is not exactly 0/1,
  an exception is raised by Drawing2D
- could happen due to rounding errors
- see svg-net#966

Source/Painting/SvgGradientServer.Drawing.cs

@@ -90,16 +90,21 @@ protected ColorBlend GetColorBlend(ISvgRenderer renderer, float opacity, bool ra
                     i++;
                 }
 
-                blend.Positions[i] = position;
+                // always set the first position to 0 to account for rounding errors
+                blend.Positions[i] = i == 0 ? 0.0f : position;
                 blend.Colors[i] = colour;
 
                 // Insert this colour after itself at position 0
                 if (insertEnd && i == colourBlends - 2)
                 {
                     i++;
+                    blend.Colors[i] = colour;
+                }
 
+                if (i == colourBlends - 1)
+                {
+                    // always set the last position to 1 to account for rounding errors
                     blend.Positions[i] = 1.0f;
-                    blend.Colors[i] = colour;
                 }
             }
 

doc/ReleaseNotes.md

@@ -5,6 +5,7 @@ The release versions are NuGet releases.
 
 ### Fixes
 * fixed issue for `SvgTextBase.Bounds` with blank `SvgTextSpan` (see [PR #963](https://github.com/svg-net/SVG/pull/963))
+* fixed crash for certain gradient values (see [#966](https://github.com/svg-net/SVG/issues/966))
 
 ## [Version 3.4.1](https://www.nuget.org/packages/Svg/3.4.1)  (2022-03-19)