one final spot where whitespace needs trimming, non CDK as well as CDK

src/SixLabors.Fonts/TextLayout.cs

@@ -1321,6 +1321,9 @@ public TextLine SplitAt(LineBreak lineBreak, bool keepAll)
 
             if (index == 0)
             {
+                // Now trim trailing whitespace from this line in the case of an exact
+                // length line break (non CJK)
+                this.TrimTrailingWhitespaceAndRecalculateMetrics();
                 return this;
             }