Add testcase for app13 marker with empty IPTC

src/ImageSharp/Formats/Jpeg/JpegDecoderCore.cs

@@ -644,10 +644,13 @@ namespace SixLabors.ImageSharp.Formats.Jpeg
                     {
                         var resourceBlockNameLength = ReadImageResourceNameLength(blockDataSpan);
                         var resourceDataSize = ReadResourceDataLength(blockDataSpan, resourceBlockNameLength);
+                        if (resourceDataSize > 0)
+                        {
                             this.isIptc = true;
                             this.iptcData = blockDataSpan.Slice(2 + resourceBlockNameLength + 4, resourceDataSize).ToArray();
                             break;
                         }
+                    }
                     else
                     {
                         var resourceBlockNameLength = ReadImageResourceNameLength(blockDataSpan);

tests/ImageSharp.Tests/Metadata/Profiles/IPTC/IptcProfileTests.cs

@@ -45,6 +45,15 @@ namespace SixLabors.ImageSharp.Tests.Metadata.Profiles.IPTC
             }
         }
 
+        [Theory]
+        [WithFile(TestImages.Jpeg.Baseline.App13WithEmptyIptc, PixelTypes.Rgba32)]
+        public void ReadApp13_WithEmptyIptc_Works<TPixel>(TestImageProvider<TPixel> provider)
+            where TPixel : unmanaged, IPixel<TPixel>
+        {
+            using Image<TPixel> image = provider.GetImage(JpegDecoder);
+            Assert.Null(image.Metadata.IptcProfile);
+        }
+
         [Fact]
         public void IptcProfile_ToAndFromByteArray_Works()
         {

tests/ImageSharp.Tests/TestImages.cs

@@ -163,6 +163,7 @@ namespace SixLabors.ImageSharp.Tests
                 public const string Testorig12bit = "Jpg/baseline/testorig12.jpg";
                 public const string YcckSubsample1222 = "Jpg/baseline/ycck-subsample-1222.jpg";
                 public const string Iptc = "Jpg/baseline/iptc.jpg";
+                public const string App13WithEmptyIptc = "Jpg/baseline/iptc-psAPP13-wIPTCempty.jpg";
 
                 public static readonly string[] All =
                 {