Fix PatternColor Equals() method and fix #1016

Author: BobLd

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

@@ -7,6 +7,29 @@
 
     public class GithubIssuesTests
     {
+        [Fact]
+        public void Issue1016()
+        {
+            // Doc has letters with Shading pattern color
+
+            var path = IntegrationHelpers.GetSpecificTestDocumentPath("colorcomparecrash.pdf");
+
+            using (var document = PdfDocument.Open(path, new ParsingOptions() { UseLenientParsing = true, SkipMissingFonts = true }))
+            {
+                var page = document.GetPage(1);
+
+                var letters = page.Letters;
+
+                var firstLetter = letters[0];
+                Assert.NotNull(firstLetter.Color);
+
+                var secondLetter = letters[1];
+                Assert.NotNull(secondLetter.Color);
+
+                Assert.True(firstLetter.Color.Equals(secondLetter.Color));
+            }
+        }
+
         [Fact]
         public void Issue953()
         {

src/UglyToad.PdfPig.Tests/Integration/SpecificTestDocuments/colorcomparecrash.pdf

@@ -158,7 +158,7 @@ public bool Equals(TilingPatternColor? other)
 
             return PatternType.Equals(other.PatternType) &&
                 Matrix.Equals(other.Matrix) &&
-                ExtGState.Equals(other.ExtGState) &&
+                ((ExtGState is null && other.ExtGState is null) || ExtGState?.Equals(other.ExtGState) == true) &&
                 PaintType.Equals(other.PaintType) &&
                 TilingType.Equals(other.TilingType) &&
                 BBox.Equals(other.BBox) &&
@@ -225,7 +225,7 @@ public bool Equals(ShadingPatternColor? other)
 
             return PatternType.Equals(other.PatternType) &&
                    Matrix.Equals(other.Matrix) &&
-                   ExtGState.Equals(other.ExtGState) &&
+                   ((ExtGState is null && other.ExtGState is null) || ExtGState?.Equals(other.ExtGState) == true) &&
                    Shading.Equals(other.Shading);
         }