Fix decoder scope issue

Former-commit-id: ca50cdd8efb68d5d312dfd8e53852d4f00c1671f
Former-commit-id: e9698d8e7c43a772280f46aabf2098897a06c871
Former-commit-id: 6ea60a611bcfca0858972a09ed43d2909b242303

src/ImageProcessor/Formats/Gif/GifDecoderCore.cs

@@ -405,8 +405,7 @@ namespace ImageProcessor.Formats
             {
                 if (this.graphicsControlExtension.DisposalMethod == DisposalMethod.RestoreToBackground)
                 {
-                    Parallel.For(descriptor.Top, descriptor.Top + descriptor.Height,
+                    for (int y = descriptor.Top; y < descriptor.Top + descriptor.Height; y++)
-                        y =>
                     {
                         for (int x = descriptor.Left; x < descriptor.Left + descriptor.Width; x++)
                         {
@@ -418,7 +417,7 @@ namespace ImageProcessor.Formats
                             this.currentFrame[offset + 2] = 0;
                             this.currentFrame[offset + 3] = 0;
                         }
-                            });
+                    }
                 }
                 else if (this.graphicsControlExtension.DisposalMethod == DisposalMethod.RestoreToPrevious)
                 {