Fix glyph bounding box for Type3 font with zero height (#610)

* For Type3 font with a zero width/height bounding box, set it to a sensible
default using the font matrix. This ensures the letter bounding boxes will
not have height 0.

* Also added a test to check for non-zero height in the sample Type3 PDF

* Prevent division by zero error

---------

Co-authored-by: mvantzet <mark@radialsg.com>

src/UglyToad.PdfPig.Tests/Integration/Type3FontTests.cs

@@ -0,0 +1,24 @@
+namespace UglyToad.PdfPig.Tests.Integration
+{
+    using Xunit;
+
+    public class Type3FontTests
+    {
+        private static string GetFilename()
+        {
+            return IntegrationHelpers.GetDocumentPath("type3-font-zero-height.pdf");
+        }
+
+        [Fact]
+        public void HasLetterWidthsAndHeights()
+        {
+            using (var document = PdfDocument.Open(GetFilename()))
+            {
+                var page = document.GetPage(1);
+
+                Assert.Contains(page.Letters, x => x.GlyphRectangle.Width != 0);
+                Assert.Contains(page.Letters, x => x.GlyphRectangle.Height != 0);
+            }
+        }
+    }
+}

src/UglyToad.PdfPig.Tests/Integration/VisualVerification/GenerateLetterBoundingBoxImages.cs

@@ -22,6 +22,7 @@
         private const string SPARCv9ArchitectureManual = "SPARC - v9 Architecture Manual";
         private const string CroppedAndRotatedFile = "cropped-and-rotated";
         private const string MOZILLA_10372_2File = "MOZILLA-10372-2";
+        private const string Type3FontZeroHeight = "type3-font-zero-height";
 
         private static string GetFilename(string name)
         {
@@ -137,6 +138,12 @@
             Run(MOZILLA_10372_2File, 1584, 7);
         }
 
+        [Fact]
+        public void Type3FontZeroHeightTest()
+        {
+            Run(Type3FontZeroHeight, 1255);
+        }
+
         private static void Run(string file, int imageHeight = 792, int pageNo = 1)
         {
             var pdfFileName = GetFilename(file);

src/UglyToad.PdfPig/PdfFonts/Parser/Handlers/Type3FontHandler.cs

@@ -31,6 +31,12 @@
 
             var fontMatrix = GetFontMatrix(dictionary);
 
+            if (boundingBox.Left == 0 && boundingBox.Bottom == 0 && boundingBox.Height == 0 && boundingBox.Width == 0 
+                && fontMatrix.A != 0 && fontMatrix.D != 0)
+            {
+                boundingBox = new PdfRectangle(0, 0, 1 / fontMatrix.A, 1 / fontMatrix.D);
+            }
+
             var firstCharacter = FontDictionaryAccessHelper.GetFirstCharacter(dictionary);
             var lastCharacter = FontDictionaryAccessHelper.GetLastCharacter(dictionary);
             var widths = FontDictionaryAccessHelper.GetWidths(scanner, dictionary);