Correctly break during Png decoding

src/ImageSharp/Formats/Png/PngDecoderCore.cs

@@ -204,18 +204,13 @@ public Image<TPixel> Decode<TPixel>(BufferedReadStream stream, CancellationToken
                             break;
                         case PngChunkType.FrameControl:
                             frameCount++;
-                            if (frameCount == this.maxFrames)
-                            {
-                                break;
-                            }
-
                             currentFrame = null;
                             currentFrameControl = this.ReadFrameControlChunk(chunk.Data.GetSpan());
                             break;
                         case PngChunkType.FrameData:
-                            if (frameCount == this.maxFrames)
+                            if (frameCount >= this.maxFrames)
                             {
-                                break;
+                                goto EOF;
                             }
 
                             if (image is null)
@@ -271,6 +266,11 @@ public Image<TPixel> Decode<TPixel>(BufferedReadStream stream, CancellationToken
                                 previousFrameControl = currentFrameControl;
                             }
 
+                            if (frameCount >= this.maxFrames)
+                            {
+                                goto EOF;
+                            }
+
                             break;
                         case PngChunkType.Palette:
                             this.palette = chunk.Data.GetSpan().ToArray();
@@ -389,15 +389,15 @@ public ImageInfo Identify(BufferedReadStream stream, CancellationToken cancellat
                             break;
                         case PngChunkType.FrameControl:
                             ++frameCount;
-                            if (frameCount == this.maxFrames)
+                            if (frameCount >= this.maxFrames)
                             {
                                 break;
                             }
 
                             lastFrameControl = this.ReadFrameControlChunk(chunk.Data.GetSpan());
                             break;
                         case PngChunkType.FrameData:
-                            if (frameCount == this.maxFrames)
+                            if (frameCount >= this.maxFrames)
                             {
                                 break;
                             }

tests/ImageSharp.Tests/Formats/Png/PngDecoderTests.cs

@@ -701,4 +701,14 @@ public void Decode_BadPalette(string file)
         string path = Path.GetFullPath(Path.Combine(TestEnvironment.InputImagesDirectoryFullPath, file));
         using Image image = Image.Load(path);
     }
+
+    [Theory]
+    [WithFile(TestImages.Png.Issue2752, PixelTypes.Rgba32)]
+    public void CanDecodeJustOneFrame<TPixel>(TestImageProvider<TPixel> provider)
+    where TPixel : unmanaged, IPixel<TPixel>
+    {
+        DecoderOptions options = new() { MaxFrames = 1 };
+        using Image<TPixel> image = provider.GetImage(PngDecoder.Instance, options);
+        Assert.Equal(1, image.Frames.Count);
+    }
 }

tests/ImageSharp.Tests/TestImages.cs

@@ -156,6 +156,9 @@ public static class Png
         // Issue 2668: https://github.com/SixLabors/ImageSharp/issues/2668
         public const string Issue2668 = "Png/issues/Issue_2668.png";
 
+        // Issue 2752: https://github.com/SixLabors/ImageSharp/issues/2752
+        public const string Issue2752 = "Png/issues/Issue_2752.png";
+
         public static class Bad
         {
             public const string MissingDataChunk = "Png/xdtn0g01.png";