Do not insert mandatory break when line is broken by wrapping.

src/SixLabors.Fonts/TextLayout.cs

@@ -1093,11 +1093,14 @@ VerticalOrientationType.Rotate or
                     // Mandatory wrap at index.
                     if (currentLineBreak.PositionWrap == codePointIndex && currentLineBreak.Required)
                     {
-                        textLines.Add(textLine.Finalize());
-                        glyphCount += textLine.Count;
-                        textLine = new();
-                        lineAdvance = 0;
-                        requiredBreak = true;
+                        if (textLine.Count > 0)
+                        {
+                            textLines.Add(textLine.Finalize());
+                            glyphCount += textLine.Count;
+                            textLine = new();
+                            lineAdvance = 0;
+                            requiredBreak = true;
+                        }
                     }
                     else if (shouldWrap && lineAdvance + glyphAdvance >= wrappingLength)
                     {
@@ -1178,6 +1181,7 @@ VerticalOrientationType.Rotate or
                 }
 
                 // Find the next line break.
+                bool lastMandatory = lastLineBreak.Required;
                 if (currentLineBreak.PositionWrap == codePointIndex)
                 {
                     lastLineBreak = currentLineBreak;
@@ -1199,9 +1203,22 @@ VerticalOrientationType.Rotate or
                     continue;
                 }
 
+                // The previous line ended with a non-mandatory break at the wrapping length but the new line starts
+                // with a mandatory line break. We should not add a new line in this case as the line break has
+                // already been synthesized.
+                if (textLine.Count == 0
+                    && textLines.Count > 0
+                    && !lastMandatory
+                    && CodePoint.IsNewLine(codePoint))
+                {
+                    codePointIndex++;
+                    graphemeCodePointIndex++;
+                    continue;
+                }
+
+                // Do not add new lines unless at position zero.
                 if (textLine.Count > 0 && CodePoint.IsNewLine(codePoint))
                 {
-                    // Do not add new lines unless at position zero.
                     codePointIndex++;
                     graphemeCodePointIndex++;
                     continue;

tests/SixLabors.Fonts.Tests/Issues/Issues_431.cs

@@ -0,0 +1,31 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+using System.Numerics;
+
+namespace SixLabors.Fonts.Tests.Issues;
+
+public class Issues_431
+{
+    [Fact]
+    public void ShouldNotInsertExtraLineBreaks()
+    {
+        if (SystemFonts.TryGet("Arial", out FontFamily family))
+        {
+            Font font = family.CreateFont(60);
+            const string text = "- Lorem ipsullll\ndolor sit amet\n-consectetur elit";
+
+            TextOptions options = new(font)
+            {
+                Origin = new Vector2(50, 20),
+                WrappingLength = 400,
+            };
+
+            int lineCount = TextMeasurer.CountLines(text, options);
+            Assert.Equal(4, lineCount);
+
+            IReadOnlyList<GlyphLayout> layout = TextLayout.GenerateLayout(text, options);
+            Assert.Equal(46, layout.Count);
+        }
+    }
+}