Fix(#499): inconsistent text height when using multiple lines

Source/QuestPDF.Examples/TextExamples.cs

@@ -974,5 +974,35 @@ namespace QuestPDF.Examples
                         });
                 });
         }
+        
+        [Test]
+        public void InconsistentLineHeightWhenUsingNewLineTest()
+        {
+            RenderingTest
+                .Create()
+                .PageSize(PageSizes.A4)
+                .ProduceImages()
+                .ShowResults()
+                .Render(container =>
+                {
+                    container
+                        .Padding(20)
+                        .Background(Colors.Grey.Lighten4)
+                        .Text(text =>
+                        {
+                            text.DefaultTextStyle(x => x.FontSize(16));
+                            
+                            text.Line(Placeholders.Paragraph());
+                            text.Line("");
+                            text.Line(Placeholders.Paragraph());
+                            
+                            text.Line(Placeholders.Label()).FontSize(48);
+                            
+                            text.Line(Placeholders.Paragraph());
+                            text.Line("");
+                            text.Line(Placeholders.Paragraph());
+                        });
+                });
+        }
     }
 }

Source/QuestPDF/Fluent/TextExtensions.cs

@@ -88,7 +88,19 @@ namespace QuestPDF.Fluent
             if (!TextBlocks.Any())
                 TextBlocks.Add(new TextBlock());
             
-            TextBlocks.Last().Items.Add(item);
+            var lastTextBlock = TextBlocks.Last();
+
+            // TextBlock with only one Span with empty text is a special case.
+            // It represents an empty line with a given text style (e.g. text height).
+            // When more content is put to text block, the first items should be ignored (removed in this case).
+            // This change fixes inconsistent line height problem.
+            if (lastTextBlock.Items.Count == 1 && lastTextBlock.Items[0] is TextBlockSpan { Text: "" })
+            {
+                lastTextBlock.Items[0] = item;
+                return;
+            }
+            
+            lastTextBlock.Items.Add(item);
         }
         
         [Obsolete("This element has been renamed since version 2022.3. Please use the overload that returns a TextSpanDescriptor object which allows to specify text style.")]